What is the most common mistake freelancers make when trying to use AI to write their client proposals?

[Btaliat]

I was on a particular freelancing where an advanced freelancer was advising the new ones that whenever they want to write proposals, they should not msnht the mistake of writing with artificial intelligence tools. They should make sure that they don't use the tools, especially for new clients. Unfortunately, he didn't say the reason for this, despite the fact that many people were asking for the reason for the advise. Is there any reason why freelancers should not make use of artificial intelligence tools to write proposals?