While true, many apps, including github, make this problematic for something like an admin account.

2FA, by it's nature, is bound to one single software, tool, or piece of hardware[1].

This limits the access of e.g. an administrator-login to one person and her personal phone, only. A bus-factor that is unacceptable to many.

Software like AWS allows more granular set-up, but still complex. Linode, Digital-Ocean and even docker.io, last time I looked, make it impossible to share the admin-account by allowing multiple 2FA devices active on one account simultaneous. And if they did, that would greatly lower the security of that account (still better than no 2fa though)

[1] 2FA, like google authenticator (or one of the much better open source alternatives thereof) make it possible to share a 2fa secret across devices, but that is both insecure and hard.