This is one of the best parts about hibernation. Shutting down is saving state. Booting? The kernel starts booting as usual, entirely the same as a normal boot. It gets quite far along, has already loaded a bunch of drivers, and then it finds the hibernation state & loads that.
Where-as with most s3 and s2idle suspends, there really is a lot of system level bios support required to make things happen. Many systems just do it wrong, not to spec, or desktops often not at all. These are non-issues in hibernation.
To your point though, I did have a laptop on which the wifi would disappear every other hibernation. I'd tend to hibernate it, immediately wake it up, and hibernate again, so when I really turned it on it would be good to go. For a while I had been packing a USB wifi card because I hadn't put it together. So yeah I've seen issues. A kernel upgrade half a decade ago seemed to have fixed that, but yeah I guess it's some evidence of problems. Still, the amount of time I've spent trying to get systems to suspend has been long & sad & difficult, with little evidence of what's happening. Hibernation has been a pretty reliable & consistent tool that I feel like I can almost always rely on.