EDIT: Job has commented in https://news.ycombinator.com/item?id=13250453
The announcement from GitHub might have triggered us. GitHub Pages was limited about 3 days go https://news.ycombinator.com/item?id=13227863
Job asked for votes 3 days ago https://gitlab.com/gitlab-org/gitlab-ce/issues/14605#note_20...
Looking at our internal chat logs it seems that the announcement got us thinking about pages again. But the decision to open source it was based on what kind of people used it (more small organizations than we thought, fewer large organizations than we thought).
I've asked Job to comment too.
BTW We're not sure if we'll limit GitLab.com Pages at some point, see "GitLab Pages with very high traffic (currently unlimited even in the free plan)" from https://about.gitlab.com/gitlab-com/#free-forever Of course you now always have the option to host your own.