And sometimes automatic updates break and then the site may be down until you find the problem which may require much reading and therefore a longer time if you don't deal with sysadmin stuff often.
With PaaS it's someone else's job who does this every day.
...so someone else can install the updates that break the server? Check your SLA, no cloud provider is going to pay you much compensation when the service goes down
With PaaS it's someone else's job who does this every day.