Flatpak is not designed to solve all the same problems as snap they have very different scopes and goals. It’s really only Linux hobbyists that see these as comparable technologies.
Also the Steam flatpak is unofficial just like the snap, they would be unwilling to support flatpak issues as well.
It’s a word that has become popular in general in the last year-ish. But if you hear it more here. It is likely because it is a term used to describe the dynamic that pushed people from Reddit and other platforms to Lemmy. So you will here it more here, since pretty much everyone here has been personally affected by it.
Basically we are a self selecting group of people who chose to leave (or minimize use of) big tech platforms. And are therefore much more likely to be aware of the problems with those platforms.