How can more instances not lead to more money? Look at the explosion of mastodon and other federated software. There's a lot of good will in the community and being a viable competitor to Github is definitely not worth nothing. If Gitlab could offload the majority of users from their main instance, I bet it would actually save them money. And more users, probably also means more contributors since they'll have experience hosting the instance and fixing issues they run into.

IMO, it's short-term thinking to say "federation is of no value to us".