It's common for the hanger to bend inwards, and there are often no symptoms initially. Your derailleur appears to work normally, but you have to shift farther than before. But you don't notice that. You don't remember the bike being banged in a self-closing door or laying the bike on its drive side or something else bumping against it. And it might get banged and bent several times before the derailleur goes into the spokes. You might even readjust the limit screws so it works properly, not noticing the bend in the hanger. I've worked as a shop mechanic, and I've seen this many times. Often the bike owner will swear with 100% certainty that the hanger or derailleur was never bent, but I've seen it enough to know what's really going on. This is why a derailleur guard is even usefuller than a dork disk, because it prevents the bending, and the bending is why the dork disk is necessary.

I don't use a derailleur guard or a dork disk, for purely aesthetic, vain reasons. If I ever take a long tour, I would seriously consider both or at least the derailleur guard.

I've been lucky. I have had bent derailleurs that I didn't know about, and as I was shifting it into the spokes, I felt it quickly enough and shifted back out before any damage happened. That's a combination of luck and good sensitivity to what my bike is doing.