* Google collects vast amounts of personal data, specifically through receiving all of your email and analyizing it.
* It builds elaborate user profiles and uses them to target you with ads designed to better influence you.
* Its hold on information (from different sources) has made it excessively powerful economically, and thus also politically.
* Google/Alphabet has long started to affect legislation, including through direct registered lobbying: ~15 Million USD in 2024 (opensecrets.org).
* It has been known to pass, and likely still passes, the information it collects - including copies of your email correspondence - on to the US government (Edward Snowden leaks).
and finally:
* There are multiple email providers, many of them quite good - both for pay and gratis. Naturally most of the gratis ones have their own interests, but nothing like Google.