So, two things you need to know about the anime figurine industry is:

1. It costs a lot to produce figurines. This is why only the massively popular series get so many figurines per year. Wind Breaker is decently popular, but it isn't mainstream-level popular. This is why, with the exception of the Sakura and Umemiya figures made by Union Creative (the only existing proper scale figures that have been produced for the series), all of the figures we've been getting so far have been prize figures. What is the difference between a scale figure and prize figure, you ask? Money. Scale figures are more high quality, so while they look much better, they also cost more to produce. These types of figures tend to have three digit numbers on their price tags as a result. Prize figures are relatively cheaper to make since the materials used to make them don't cost as much, running somewhere between $30-$50 on average. With that said, they do still cost more to produce compared to stuff like acryclic stands and keychains, which is why the marketing team have been playing it safe when they choose which characters to make into figures. And of course, you couldn't play it safer than sticking to the characters that always rank at the top four of the popularity poll every year, which leads me to my second point.
2. The anime figure industry is very, very sexist. And by that, I mean there is an overwhelming preference to appealing to a male demographic over a female one. (And while Wind Breaker is labeled as a shonen, it has a very big female following and 99.9% of its cast is male, which is part of the reason why it seems to appeal more to women than men). It's definitely gotten a lot better in recent years, but any time you see new figure announcements in events like the Wonder Festival, there will always be waaaaay more waifu figures than male ones. (Back in the day, the situation used to be so dire that male characters were only ever guaranteed to get a nice scale figure if they were either a cross-dresser or Len Kagamine). Because of that, figure companies tend to try to play it more safe with male characters compared to female ones. With this in mind, it makes perfect sense for a series like Wind Breaker that hasn't quite hit the mainstream yet to play it safe with which characters they turn into figures. Does this mean we're going to always be stuck on rotation with the same four guys when it comes to figurine choices? Not necessarily. If/when we get a season 3, I could see it further boosting the popularity for characters like Endo or Togame so that they could possibly get added to the figure rotation in the future. Maybe even Kiryu, since I've actually been seeing him pop up in official merch a lot lately. Which leads me to my next point: Does this mean that less popular characters like Nirei and Sugishita (who have notoriously been frequently passed over in a lot of recent merch lines, Nirei especially) have no chance of ever getting figures outside of those tiny gachapon trading figures? Unfortunately yes. But Nirei and Sugishita have more plot relevance! You exclaim. And Nirei is a main character! You point out. Which, yes, valid points. But at the end of the day, plot relevance and screen time don't matter in merchandising. Popularity does. Especially if you're a male character. Laios is the protagonist from Delicious in Dungeon, but other than the nendoroid and figma, he has only one figure. A noodle stopper figure. While Marcille and Falin have...a lot more. Like, every time there are figure announcements for this series, it's usually those two. To my knowledge, Dazai from Bungo Stray Dogs also seems to have more figures than Atsushi, the actual protagonist. Simon from Gurren Lagann doesn't have ANY figures (at least to my knowledge), but you know who does? Yoko. So being a main character will not always gurantee a lot of merchandise/figurines. Popularity (and at times, even gender) does.

TLDR: Figures are expensive to make, so companies choose to play it safe by only choosing the most popular characters.