The effort required to set up an appropriate hosting account is still orders of magnitude more work than filling out a 5 line form.
The point is that it demonstrates a bare minimum of technical competency, whether that is innate technical knowledge, or just being able to research a problem and following instructions. It's an unspoken interview question before anyone has even looked at your resume.
Again, if your primary job is a window cleaner, or a plumber, or anything else non-technical, then it doesn't matter so much as long as your email address isn't "email@example.com" as someone else pointed out.
But if you are in some kind of techncal role, and the best you can do is gmail address, it demonstrates that you are either not as skilled as you claim to be, or you simply don't care enough to eat your own dog food. Either way, I *will* hold that as a point against you, because the last thing I will do is choose to willingly work with anyone that has either of those qualities.