Article leaves out cost of migration. If you're trying to get better uptime, you're likely going to incur a downtime migrating everything over so you've already taken a few step back uptime wise unless the platform you're moving off of is already horrible.

The article touches on it, but there's also compliance concerns (access control is mentioned, also retention policies, DR, ability to redact/remove improperly added data)

They briefly mentioned monitoring but, like auth, can be non trivial for a well built system. Something like email is easy until the entire system is down and the alerts don't go out anymore (so you need an external monitoring system)

I also don't see labor cost mentioned very often. How many hours will it take to support?