GitLab has an explicit program for approved Open Source projects:
https://about.gitlab.com/handbook/marketing/community-relati...
This is their philanthropic effort. They need to remain financially solvent to provide anything long term, so of course they need to be careful how much they're giving away and for how long.
If you're not in the approved open source program, you should consider your usage of the "Free Tier" as part of their freemium business model whereby they hope to convert you at some point into a paying customer.
> GitLab should seriously re-learn what's more important for their service: user engagement or the code hosted on it.
They're a business that needs to pay the builds (including the long-term costs of storage). If they haven't approved your projects into their open source program, you should consider paying them to host the code.
I have my own issues with GitLab, but I won't judge them for the need to pay the bills.