I too would like to understand why. Perhaps the only one I care for is that I would not like to give too much power to Microsoft in choosing who can contribute.
Others have issue with their code being used in AI training, but I find no issue in that myself, my code is not exclusively mine anyway and I have no say in how it is being used.
I'm banned from GitHub because I didn't give them my mobile phone number, but I wouldn't switch to another provider that could easily do the exact same thing - "fool me twice"
No AI, EU based, so respects the GDPR for all users, regardless of where they live, you can send PRs to make it better, is 100% Free Software, has its own Actions system that is also 100% Free Software, the logo is nice, you can become a member of the Berlin based association and have a direct vote on policy/feature changes.
