That's astute of you to notice that discrepancy. It's actually two different things altogether.
For my phone, I *must* have a Google Play account (which we previously discussed is a requirement). *That* account is the one that I constantly delete and create a new random one periodically. That account knows too much about me and what I do, even though I am probably unique in that I turn off *everything* that I can figure out how to turn off with respect to location services and tracking and syncing, etc.
But I have a *real* email account, which is Gmail, which, up until extremely recently (within the past few months) allowed me to log in without ever having provided it a phone number.
I access *that* real (permanent) account mostly on a desktop, but I can also access that real account with K9mail or any MUA on any platform (I just can't use the Gmail app on Android).
I see no advantage to Google other than they have a nice mail service (which is getting worse lately due to the recent need to give it a phone number).
Encryption of email is/was a great idea, since Phillip Zimmerman days, but it's still impractical, because everyone would need to do it. And they don't. So it's not practical.