You can thank all of the disposable email services
The unfortunate reality is that if third party disposable email services didn't exist then it wouldn't have such a distrust for random domains. Anyone can just throw up an email service on a new domain and then anyone can start using it for fraud and abuse. If you've never run a freemium service then you might not know just how wide scale this sort of fraud is
I went into internets in 1995. Must I tell you about fraud and abuse in early 2000s?
Blocking domains is a cheap shot. It ticks a box somewhere maybe, but it does not and can not prevent or mitigate.