More and more of them are doing it b/c they're noticing that a "one time purchase" isn't enough to cover costs. You tend to get lower quality software. Especially prevalent with games where they use some "cookie cutter template" to churn out a game (usually some clone), then move on to their next app, and not really supporting previous ones since that costs time they're tight on (unless not doing some minimum would cost them more). I recall a podcast where they said subscription really is the way to go. If you're doing premium pricing, apps should be 5x what they are now (so say, not $5, but $25. $10 to $50)
However, despite some doom and gloom that there won't be any non-sub apps left, not all apps are popular enough to go this route. I'm subscription averse as much as the next person is, but if you really do use something you like, a sub may not be such a bad way to go. If I didn't already have Office 2016 as part of the Microsoft Home Use Program, I probably would've gotten a Office 365 sub for my PC. I make sure to write down all my subscriptions to keep track of them. Software, streaming services, Costco membership, Sirius XM, etc. Helps you keep track, and if you want to analyze, go there to see what you really do need, vs. stuff you can hock.