It's super useful for a few sites I visit frequently who require 2FA but I don't need that security. But yeah, otherwise it's a pretty remarkably bad idea.
When you sign in to a website from your phone using a saved password and use that same phone for 2fa, it's pretty much the same thing.
The whole meme that saving the 2fa seed to password managers is a bad idea needs to die. Most of the advantages of 2fa are still present when using a password manager.