"Everyone else is doing it" doesn't make it right.
It also makes it dangerous to become dependent on these services. What if at some point in the future, your provider decides that something you make competes with something they make, and they cut off your access?
When that provider's ToS allows them full access to the inputs/outputs you're sending through their system, there is a strong incentive to build something competitive with you once you're proven profitable enough.
I don't know how companies currently navigate that.
It also makes it dangerous to become dependent on these services. What if at some point in the future, your provider decides that something you make competes with something they make, and they cut off your access?