E-mail clients don’t serve ads.
For security reasons, they block linked content by default, meaning google can’t track what I do with my e-mails.
Google can terminate an account any time without any reason, if they do that, I won’t lose access the e-mails I’ve received or sent.
My screen refresh rate is 60Hz, ping from here to gmail.com 36ms, this means web interface has at least 3x latency compared to a locally running app.
I don’t care about their web interface re-designs, or browser compatibility issues like the one discussed.
Gmail can’t turn off IMAP as it would break e-mail on smartphones. Large share of these smartphones run old versions of Google Android which will never be updated, this also helps to ensure their IMAP access is here to stay.