No, I'm sorry, I do think this is an attention span issue. You say there's no virtue in suffering through boredom, but a few minutes of scene-setting should not feel painful.
Yes, some movies are boring, but those are bad movies. Turn them off. Good movies are made by skilled directors who know better than to stick a big boring part in the middle. Taste is subjective, of course, but the middle & the end get made by the same person. If the middle isn't enjoyable, the end probably won't be either; by the same token, if you consistently need to skip through the middle parts of movies with great endings, you're probably skipping good stuff which you might enjoy if you had a greater tolerance for slower, more atmospheric cinema. It might seem like sitting through the slow parts of a movie would make the experience of watching it worse, but I've found that resisting my urge to pull out my phone during slow bits has made me enjoy movies more.
Habitually, I spend a lot of time with headphones on, listening to podcasts and videos and such. I find that if I do too much of this, though, it starts to get me down. Often the best thing for my mood is to take off my headphones and just sit with my thoughts for a while. I know what you mean by "suffering through boredom," but it doesn't need to be painful to sit & do nothing for a bit. Once you get used to it, it stops feeling so uncomfortable.