Any reason why? Even if we do that it will still be possible to use backup codes to disable/change MFA, which can also trigger generation of backup codes.
Just as another security feature.
Say that somehow someone gets access to a set of backup codes I have.
If they are able to constantly regenerate backup codes, they could quickly but inconspicuously drain my balances until I realize someone has access to my account.
By disabling changes of MFA with use of backup codes, it limits a hacker as to what they could do with my account.
But it's the main purpose of backup codes. They're the only thing that allows you to disable/change your MFA method in case you lose your phone or email access or whatever.
Even with that feature blocked, hacker can use backup codes to get one of your API keys and use that to slowly drain your balances.
EDIT: also to know that someone has access to your account, you can enable Login notifications in your Security settings.
Yea ok, my idea was dumb rofl.