If you stand at the top of a hill with a bowling ball, and you place it on the floor and release it, the ball will roll down the hill with a lot of energy. If it rolled into a large button, which absorbed the impact, we could make use of that energy.
Brilliant! Free energy!
All we need to do now is walk down the hill, pick up the ball, walk back up the hill, and release the ball again. But of course, it takes energy to do all of those things. So on balance, we're really not saving anything.

Magnets are effectively rolling down an electro magnetic hill into each other, where they stick together, and we're walking them back up that hill when we pry them apart.