PCs are orders of magnitude more complex, with a lot more to break. Sounds like a whole lot of work for… what?

Assuming the internet connection and AWS work of course. Which they won’t always, then oops.

A large number of embedded micro controllers are just PCs running Yocto linux configured as GP said. You can save money with a $.05 micro controller, but in most cases the development costs to make that entire system work are more than just buying an off the shelf raspberry pi.

If you're relying on AWS you either way have a "PC" to relay communication between AWS and the keycard readers & door latches.