I don’t see how you wouldn’t have your email on an email providers servers - that’s how email works. You send an email via a provider, they forward it to the destination address you’ve included with the email.

Email is old, so the fundamental mechanics are pretty simple, and encryption wasn’t an option at the time - so it’s sent in the clear. Otherwise it would require both sender and receiver (either at both ends, or the servers) to agree on an encryption to use.