Why climb a mountain, or fly to the moon?

Because it's there.

It's a great challenge that hasn't yet run out of new places it'll run.

I can say that the first time I ever ran DOOM, I was blown away because I had no idea my computer could even do that. The game is forgiving of poor specs, even though it is in 3D space. So it runs on just about anything.

Got a new microcontroller? Sweet, does it run DOOM?

The answer is either a) of course, or b) not yet. What a great challenge that sometimes really surprises.

There is a saying

"but can it run Doom?"

Because when Doom came out there were a lot of systems that could not do so. So the question was asked a lot and it became embedded in computer culture. Then came the hackers that realised that you get cred by actually running Doom on systems that it was not designed for it. Thus culturally it was passed down over time.

Note that the phrase which came later "but can it run Crysis" is similar but Crysis doesn't have its code under an open source licence.

This is the kind of answer I was looking for. Thank you!

I think the nature of DOOM's uncomplicated engine makes it easy to port. You don't need special hardware to draw it's graphics, and there's not even a Z-buffer to render on-screen. The folks at ID also make an effort to open-source a lot of their older code, which makes the process of porting DOOM fairly easy.

That, and the game still rules. I'll find any excuse I can to get people excited about Quake again...

It’s at a level of technology that it’s possible. All the level files are open source. It really is a good game.

It's a challenge of one's programming ability. The more obscure the device, the more brownie points you earn.

Once upon a time, the question about the quality of a computer's PC-compatibility was "Will it run "Microsoft's Flight Simulator?" ".

It's the computing equivalent of the Big Mac index.

A real star field that is pixel perfect on any device running Elite would be the Quarter Pounder index with fries and pop.

I assume people just do it mostly for fun but perhaps also to push some weaker hardware to its limits or to demonstrate portability.