I'm fairly confident most people could do most things if they really wanted to, but it seems like most people don't. This is partially a function of time—no one has the time to do everything in the world—but I do wonder about the people who seemingly don't do anything well, or who don't believe they can do anything well. It often seems like they haven't really tried.
A human lifetime is obviously too short to learn to do everything well.
But many people waste a lot of the time they do have in their life -- playing mindless games, reading/watching absolute trash, surfing the web or any number of other absolutely useless activities.
It's very difficult to really dedicate yourself to getting better even at a single skill over many long years. There are always distractions and a lot of boredom and self-criticism to overcome. It's painful and hard, and many people just don't have the willpower to do it.