[Speculation:]
Perhaps they've run the numbers and can figure out that they make enough money from enterprise clients and will make enough more money from the 'marketplace' being a channel for selling github integrations and addons to cover this cost of not trying to monetize through supporting teams.
It also moves a large base from 'customer' with needed support to free users which don't need the same level of support.
E.g. I have git repos where I use multiple remotes (1 Github, 2 Gitlab..). So git is the same as everwhere.. I never felt locked in. It's not too hard to transfer your repos to another provider.