Hibernate eventually began posing trouble for a few reasons. Firstly, as memory sizes increased, the time to hibernate became longer as you had to entirely serialize memory to disk.

Secondly, the number and types of peripherals were tricky to reconstitute and grab the state of, and this made working with the OS tricky. It would be possible that an application might be in the middle of an operation with a device that was no longer present, for example.

Sleep was easier, and yes, it "just worked".

It feels as though laptops are less functional now than they used to be because of stuff like this!