Context: An external contributor is taking it upon himself to implement ActivityPub and possibly ForgeFed in Gitlab after Gitlab ignored the issue for more than 7 years
Now another 7 years and 24 "please rebase this old code" requests before it's merged
GitLab don't have the monetary incentive to implement federation. Most of their revenue is coming from big companies which are mostly using private GitLab instance and won't want their projects federated.
That being said, hope this changes can get merge as somebody already done the dirty work for them. The beauty of open source.
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".