ISP free email
Yes most ISPs do provide free email but to them:
It's a cost centre not a revenue generator, a black hole for them to pour money into.
If you move ISP you lose the email address (maybe after a period of grace). That means you've got to change all those places where you registered and they use it as your contact address, and your personal contacts. For me that list is in the hundreds.
If there's an outage, its a free service so not imperative to fix urgently. Real life examples abound.
The spam filters are notoriously poor, the worst issue being false positives, mail you want being treated as spam. If you're lucky its in a spam folder so you stand a chance of recovering it but it may just be trashed or bounced.
Are any ISP email accounts as feature rich and versatile as Gmail? None I've seen come close.
BTW I believe my ISP provides free email accounts that are in fact gmail but with the branding changed, I guess they pay google a few quid a year per user and that's cheaper than trying to maintain a system themselves.
I use gmail with my own domain name, the adverts are not intrusive and if they want to read my christmas round-robin email, great, none of the intended recipients give a damn about it. If I were concerned about confidentiality of a message I'd use encryption, if I had significant volumes of confidential email then a commercial email provider or my own mailserver too. But if GCHQ want to read my messages I'm sure they'll have little difficulty intercepting them whatever I do.