Is it possible that a bunch of free stuff where they don't sell you as a product (and maybe even when they do sometimes) just isn't a viable thing to do on the web?
Generally on the web we as consumers seem to cycle through these companies, often pay nothing, and we're bummed each time they quit doing the thing...
It's possible, though that doesn't really apply to a company who made $4.34B in gross profit in 2021. I'm sure they will save some money but by making this move they are signalling (intentionally or not) that Heroku is on life support and they don't care about developers anymore.