Other reasons:

• Way too many character concepts to use as a player.
• Nobody else has the time and rules-knowledge to run a campaign.

Because I like to throw situations at players and sit back and watch them fumble the execution and yet always come out on top.

When I'm DM, I'm always in the spotlight.

/s

This is mostly a joke. But my attention wanders when I'm not involved in the action for too long. I'm more entertained as a DM.

Makes me happy that some people can enjoy being DM because otherwise I wouldn't be able to play. I'm often too worried about messing with people, and my sense of mischief works better when it's my own character I'm getting into trouble.