We use SendGrid for transactional email, but handle (solicited) bulk email in-house. The centralization of email is at least partly due to the fact that ensuring email gets delivered is difficult and time-consuming.
While I'm sure a lot of SendGrid's customers don't want (or don't know how) to configure a mail server, there are other customers who know that delivering email isn't as simple as installing Postfix. The rise of centralized email services is the inevitable byproduct.
Yeah, I know. Not blaming SendGrid in the slightest. Spammers have spoiled it for us all. Freedom disappearing because of a minority of abusers seems to be a common pattern...
While I'm sure a lot of SendGrid's customers don't want (or don't know how) to configure a mail server, there are other customers who know that delivering email isn't as simple as installing Postfix. The rise of centralized email services is the inevitable byproduct.