Why are there so many villains that are perfectly capable of defeating heroes but they get their ass beat always? It is either because they are dumb,cocky,have no experience,have no training or any other reason.The least you could do is train in preparation for your next fight but NOOOOOO.The heroes always have more experience and training and skills.
The whole point of a superhero is to give a sense of empowerment and inspiration to the reader. If the hero got his rear frequently handed to him by more powerful villains, that would not help. While that might make a good story, it doesn't necessarily make a great HERO story. So how do you make the hero win? What's the easy way to do that? Simple: Make the villain weaker than the hero. But a villain whose substantially weaker than the hero and can be easily dispatched again doesn't make a good story: they're just a thug to be beaten and ignored. So the villain has to be two things to provide decent conflict: They have to, in some way, be more powerful or superior to the hero in some way. In characters like Lex's case, he may be inferior to Clark in most instances, but he's politically and financially superior to Clark. The second thing a villain must have to be a decent conflict is a fatal flaw that results in his failure. Something that allows the hero to overcome the enemies superiority and win. The result is any villainous victory is temporary, and the hero must always win.
As for a more in continuity explanation for villains: Villains have a number of reasons for being villains. For most, it's a case of arrogance: They believe they're due what they steal, or that the world is inferior to them so they deserve to rule it, etc. Doctor Doom, Doc Ock, Norman Osborn, Lex Luthor, General Zod, etc. This arrogance results in them thinking that the hero always cheats to beat them, because in their minds, they are perfect, infallible. Again, we'll use Lex as an example: He's aware that Superman is his physical superior, but he believes his brains makes him Superman's moral and intellectual superior, therefore Superman beating him is merely a thug smashing his stuff. They don't train to beat their enemies for the same reason they don't give up a life of crime: They're just taking what they're owed, so anyone who tries to stop them is wrong. In their minds, THEY are the heroes of the story. And the hero always wins. So, since they think of themselves as the hero, and as I've said, villainous victory is always temporary, they think they must win sooner or later.
Was that a sufficient explanation?
Different reasons for different villains.
Magneto is too stubborn to look at the big picture
Joker is only in it for anarchy
Doom is much too arrogant and doesn't analyze all the smallest details
Luthor is too crazy to keep a level-head when he's winning
Loki is too immature
I could go on and on, but as badass as most of the villains are, their shortcomings always come back to bite them in the ass.