Two reasons. 1 its not free and 2. unless you're paying for top tier hosting, you can expect your emails to be rejected by large numbers of people (particularly corporate recipients) because nobody trusts email anymore and the anti-spam countermeasures have made using email a big pain. Even at work I occasionally have to send people their proofs or what-not via the company's Gmail account because the security and anti-spam countermeasures set up on their email server dump mail from our domain (and this is using GoDaddy as a host, which is less likely to be rejected ... my wife uses some cheap off-name hosting service and about a quarter of the people she tries to email with it reject her email).
As for moving email service, I'm considering ProtonMail as it's encrypted and they have a free option (although the pay one is only 48.00 € /Year)
Oh and I forgot to mention web browsers (as Chrome is Google and Mozilla is just about as bad as Google). I've been experimenting with Brave and am just about to make it my default (wish they'd hurry up with some extension support). Its lean, mean, fast and started by Brenden Eich.