There are more options than that, and I see your point.
To take the contrarian stance though: SSO not being paid is kinda nice, and not having yet another password for something is nice. —- double and: then not being able to leak a password or handle 2FA, instead focusing on their actual product.
For free users, it's pretty much just G, MS, and GH (which is currently the only "tolerable" one, but there's no reason why it won't turn into a MS account in the future just like how they killed Minecraft)
To take the contrarian stance though: SSO not being paid is kinda nice, and not having yet another password for something is nice. —- double and: then not being able to leak a password or handle 2FA, instead focusing on their actual product.