This might be a piece of news I missed, because I havn't been a Gmail user for a long time.

It looks like Google is now claiming that Thunderbird is an "insecure app" and turning off IMAP support - with predictably dire consequences for non-techy Gmail users who use Thunderbird as a client.

So it seems that Google is doing similar monopolistic lock-in stuff that Microsoft pioneered. Thunderbird of course doesn't display ads and so this is why Google want Gmail users using the web interface or some official Google email client which does show the ads.