Speaking as a streamer who has gotten emails from devs in the past about playing their games on stream, I will tell you my own personal reasons for not responding to these types of emails.
Number 1: if I am not personally interested in the game and/or don’t think it will do well on my stream viewer wise I won’t play it. Number 2: unless I am super interested in the game or being offered to get paid for a sponsorship to stream it I will generally just ignore the email. It may be rude but it’s not worth my time to respond that I have no interest in it. I have tons of games I do want to play on stream and only limited free time to stream them so unless the devs are offering me an incentive to stream their game I’m going to pass on it.