There is a huge FOSS store. In fact, it’s been the default for obtaining software for over two decades now. It’s called “just download it from the website”.
that model works to onboard a sector of the pie, the experience of hunting and pecking through a store is a familiar experience, mimicking the array of icons UI so common to phones, and app stores. having a "store" brings all the various ...downloaditfroms... to a centralized place of one stop shopping. thats the level of convienience expected by general consumers, and thats required to make the wedge of the pie widen and become a little more stable. The bigger issue is that FOSS is seen as difficult, dangerous, what hackers do, etc due to marketing forces, and the effort to keep people safe from the internet