Perhaps not serious, but I think people gravitate towards older systems these days because they are easier to conceptualize. It's not unrealistic for a single person to have a complete grasp of e.g. the C64 and it's programming environment. DOS is similarly constraint, but also easier for you to form a more or less complete mental model around.

Some people love computers and making them do weird stuff, older computers make certain tasks feel more manageable.

Most computers in Turkey come with FreeDOS preinstalled because there's a law that states all computers must be sold with an operating system. FreeDOS turns out to be the cheapest and easiest.

That's why you don't let people who have never touched a computer write tech laws. You get results like this.

Who said anything about "serious"?

(FWIW: I suspect there are more than a few old industrial control systems and such out there that are still running DOS, just because of an "if it ain't broke, don't fix it" attitude)

Because it's fun, at least for certain folks? Crazy, right?

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The real question is "why not?" :)

There's a lot of interesting projects and even innovation going on making new games for old PCs/consoles. James Lambert and Kaze are doing fantastic work in the N64 space as one example (watch their videos on Youtube)

There used to be stock exchanges running happily on DOS. Maybe there still are.

SDL is written in C. So it can support it without too much trouble. And some people are compiling stuff to run on DOS. So it makes sense. And your objection doesn't hold any water.

because you can

Uhm... excuse me? Why? Is there anyone even using DOS for anything serious these days?

Translation: "Stop liking things I don't like!"