Because it just creates more problems and work. In our small SaaS we were saying to users why they are banned: spam, abuse, fraudulent cc, etc. and that created just more work for us because these users will then write ‘reviews’, emails, etc how they are not spammers and how we are bad company. Better to lock them out and move on.

Of course, we are small SaaS and not Google but sadly I’m not aware of a better solution.