I'm a classically trained singer and many instumentalist colleagues of mine consider the voice the most difficuicult to learn amd develop as you can't see it. You have to learn by feel and sensation. It takes years of doing vocal excerciss to strengthen the muscles to sing opera for instance. It's like an athlete.
That's true I'm of the bel canto school, and I think fully dominating the voice requires a lot of hard work and intelligence, most singers (specially pop) do not take the time and do not care enough to learn to control the voice to that level, but of course the fans wouldn't know the difference, a lot of them think the more painful and out of control the more "soulful", and the more controlled the more "cold".