Why DM?

Let's be honest: being a DM or a GM is a huge pain in the ass. It takes a surprising amount of work to prep before each game: designing combat encounters, designing social encounters, building cities, creating memorable monsters and NPCs; usually all for naught because the players will deviate from the story in your mind at the drop of a hat.

They'll suss out your villain within 5 minutes, they will bend probability and crit your "boss encounter" out of existence in 2 rounds, they'd rather cause a bar fight than talk to magnificently, hand crafted NPC.

Then there is the hours you have to invest initially to know the rules. A lot of reading, both online and off; a lot of hands on experience in past games; constant gathering of information just to be able to use the system to progress the story you want to progress.

And then the story. Waiting, watching for the moment of inspiration that catapults your mind down the adventure track; sometimes even actively seeking the the inspiration: through novels, music, movies, day to day conversations. Fleshing out the details, the characters, the politics, the events. Crafting a living, breathing world for your players to explore and help you define as they explore. And more likely than not, the players will want dungeon crawl after dungeon crawl.

Why do all that? It sound like a ton of work (It is). I do it because I enjoy gaming. The more time goes by as a DM, the more I enjoy it. I enjoy creating the framework of a world and having my players explore and discover the details. I enjoy the cheers after a difficult combat and the scowls at a despicable NPC. My running a game provides an excuse for my friends to get together on a nearly weekly basis. I enjoy the plot twists and the surprises, the reveal of the plan, the demise of said plan after the PCs are done dungeon crawling. I do it so that my players can game. I do it so I can game.

Perhaps I do it for the game?

Although, having my players stick to my plan every now and then would be nice. I've put a lot of work into it.