[rlpb]

Without widespread U2F support, the list of individual MFA secrets I would have to maintain would be unmanageable. It's not yet reasonable to expect users to have MFA on all of their accounts; only their most important ones.

[stephenr]

I have MFA setup for 29 things, and I don’t really see how adding another 229 would make it any less usable.

It’s arguable that something like u2f is more secure but with a good TOTP app usability is not the problem.