My IT team is not going to break something on the most important day of the month for my business. Sometimes even when I want to do something mundane on the network, it's "eh, let's wait until not (insert key date here), just in case". Amazon does not care what day is important to my business, they're Amazon and they do what they want.
You are going to pay IT staff either way, if it's your own hires (or an MSP), or you are paying via AWS fees. If you're going to pay for IT, why wouldn't you pay for IT that takes orders from you and cares about your business?
The other thing is, Amazon's maintenance and upgrades is based around Amazon's need to remain competitive and turn a profit, and to support businesses other than yours which may have larger needs. (The rollout of a new feature that causes an outage for you might not have any benefit to you anyways.)
Similarly, a single patched Exchange server running on a single VM on a VM host with a UPS backup on it is generally speaking, more reliable and has better uptime than Office 365. Hilariously, Office 365 also costs a lot more.