I do.
As a player I can focus on my own character and on whatever's going on around it, and otherwise switch my brain off - particularly if I'm playing a dumb Fighter and-or when my PC isn't involved in the action of the moment.
But as DM I have to always be aware of what the party - and each PC - is doing, of what the game world is doing around them, of where the PCs are on the map, and of the personalities and reactions of any NPCs they meet. I also have to know the mechanics of whatever foes they're fighting and play those foes as best I can.
Add to this I also have to take notes on proceedings (my memory's not that good!), while at the same time trying to "read the room" and assess how the players are responding to whatever's going on. And sometimes be a referee.
In short, I need to be "on" a much higher percentage of the time when DMing than I do when playing.
Further, while a player can largely ignore the game between sessions if s/he wants, the same isn't usually true of a DM. Sure there's some who can wing everything on the fly, much like a rapper who makes up the words as he goes along, but those are a rare breed: most DMs, like most rappers, have to prep what they're doing at least to some extent.
This presumes having players who are willing to take on these sort of tasks. Not all are.