When online retailer ModCloth opened its first brick-and-mortar store in Austin, Texas earlier this month, it decided to offer all of its available styles in sizes XXS to 4X. For a fashion retailer, it was a rare move.

Thanks to testing products in pop-up shops for the past 18 month and constantly monitoring online consumer shopping trends, the vintage-inspired clothing label saw a demand among its female shoppers for styles in a broad range of shapes and sizes.

Yes—gasp!—larger women do want fitted clothing in current colors and the latest prints. However, brands and retailers offering such styles are few and far between.

Traditionally, plus-size collections are completely different than brands’ offerings in straight sizes (the industry term for sizes 0 to 4). What’s more, if they are housed in-store (a number of brands only offer plus-size styles online), they are almost always tucked away in the back.

“It’s almost inexistent,” said plus-size model Clementine Desseaux, of the plus-size department. “When it is there, it’s always at the back of a store, mixed with maternity clothes and isolated. There’s no sales person to take care of you—it’s hard,” she said.

Recently, Midwest supercenter Meijers received a lot of media attention for its decision to scrap its plus-size section and display all sizes (S to 3X) in one area—which highlighted the fact that the move was a big deal and signaled there’s a long way to go.

The market’s there, why aren’t the brands?

In October this year, sales of plus-size apparel for women and juniors hit $21.1 billion, up 7 percent from 12 months before—yet brands aren’t rushing to cater to it.

“The plus-size market has constantly been underserved,” said NPD retail industry analyst Marshal Cohen, adding that 35 percent of American women wear plus-size tops or bottoms, or both, yet the styles only represent 15 percent of the total market. “There’s an opportunity to grow the market, but they never focus on it,” Cohen said about brands and designers.

He also said that most brands’ and retailers’ attitudes toward the market haven’t changed in many years. “30 to 40 years ago, I talked to a combination of designers who said, ‘No that’s not for us. We don’t want our signature item, dress, outfit walking down the street being worn by a plus-size model.’ They feel as if it’s not fitting to the image of the brand they want to portray,” he said, adding that unless plus-size is a big part of a business, it’s usually the first collection to be dropped if a company is looking to save money.

Desseaux put it more bluntly: “It’s like a disease section. No one wants to show they’re creating plus sizes for women.”

However, a designer for a contemporary label, who wanted to remain anonymous, claimed the reason their line only goes up to a size 10 is because of a lack of demand.

“The buyers at stores are the ones who put in the sizes—we don’t dictate that. We give them the option. We make very few of the larger sizes mostly because, apparently, we don’t have a customer who’s buying our clothes in that size,” she said. “We have a history of making XS through XL, and then all of our XL styles end up in the warehouse because no one purchased them.”

Change is coming, albeit slowly

Offering larger sizes in styles women actually want to wear is slowly starting to catch on, thanks to newer labels and retailers who are beginning to realize the demand and business opportunities within the plus-size market. While most brands stop at sizes 12 or 14, companies like Modcloth and New York–based label Of Mercer, which recently extended its sizes to include 00 to 20, are driving change. Similarly, plus-size stores—including online retailer Eloquii, subscription service Gwynnie Bee and Lane Bryant—are also offering extended sizes of their main clothing collections.

But those who are moving into extended sizes say it isn’t easy or cheap.

Modcloth has made a big push to close the gap in its size offerings over the past two years. Today, more than half of its dresses, skirts, tops and other pieces—over 1000 different styles in total—are available in sizes XXS to 4X. In addition, the retailer ditched the “plus-size” tab on its website a year ago, despite it being one of the most common search phrases driving consumers to its site, according to the company.

“It’s been a tremendous amount of investment and work internally,” said ModCloth CEO Matt Kaness.

Extending sizes of the same collections means working with multiple fit models and is equivalent to having two separate lines, he said. This is because the pattern based off of a size 2, for example, can only be scaled up to a certain extent. After a size 12 or 14, measurement increases occur at different rates. Bust measurements grow at a quicker rate than shoulders, for example.

“We have a single-line plan, from a design perspective,” Kaness explained, “but as you get into product and tech design, everything doubles. You’re doing all the same work twice for the same design.”

Brands need to go further than just use plus-size models

Plus-size models are becoming more common in brands’ campaigns, although one anonymous model said they’re still utilized for a “wow factor.” For Desseaux, the days of using plus-size models but not following through with putting product in stores is not good enough.

“Brands are surfing on the wave of plus-size and inclusivity, but they don’t follow up in stores. They need to make clothes for bigger women and sell it in stores,” she said. “It’s all on the surface—there’s no real change.”

Perhaps quicker change lies with those who can buy the clothes and sell the pieces they select. Take Rent the Runway, for example, which has always made larger sizes available to rent both online and in-store; since its launch, the rental company has offered sizes 0 to 26. The seven-year-old company, which has six million users (self-reported), is now attempting to use its size and purchasing power to get designers it works with to cut larger pieces. Its CEO, Jennifer Hyman, said data shows that brands which only cater to plus-size women are not as popular as designer brands who create a full range of sizes.

“No one wants to feel different,” she said. “Having separate plus-size sections of a website or a store is a relic of an era of retail that the customer no longer wants to be in.”

Images via Of Mercer.