I started learning to paint a few years ago. I did not spend too much time on art history and theory. I however copied a few paintings over and over. I learned to copy them perfectly. What am I missing?
Ok, loose analogies aside, and ignoring the fact I cannot paint, here's a few thoughts:
Where are you now? You've learnt how to coordinate your hands. You've learnt how to watch someone else play, and you might have learnt how to match their hand movements to the sheet music notation. You know what the piano sounds like, and feels like. And you know what sort of music you like to play.
Where to from here? Can you play pieces that do not have tutorial videos? Can you read sheet music notation? Or can you play one by ear, with no notation to help? Can you write down what you hear? Can you write your own music? Do you know why some notes sound good to you, and others don't? Can you play fast and fluently, without tiring? Can you write music for other instruments? Can you teach other people? Can you play different styles of music, from different countries or centuries? Can you play in a band, and make music together with other people? Can you play and sing at the same time?
"No, but I don't care" is a valid answer to all of those questions, by the way. But maybe something does spark your interest.
Music is a lifetime pursuit, if you want it to be. There is always more to practice, more to learn. You don't have to do that. But you can, if you want to, and if you put in the effort.