Earlier quoted context omitted.
Fastmail and protonmail offer a lot more than just postfix+dovecot hosting. Fastmail developed new standard, brand new webmail UI, brand new webmail client. That's a lot of added value. Protonmail is heaven for crypto nerds which has its own intrinsic value as well. Ordinary mail hosting is nothing special. Anybody can do it with very little investments. Of course if they can charge for it, good for them. But I don't…
Fastmail also includes DNS, a few GB of storage and optionally static web hosting from said storage. They're also providing you with a caldav server for synced calendar, notes and contacts
Tasks can also be synced over Fastmail servers, though they do not provide a UI for it.