For the same reason people like the hiss and pops of a record, film grain, or even VHS tracking artifacts. Yesterday's technical limitations become today's aesthetic.
But the real answer is they aren't inherently bad. People don't actually need it to conform to the past limitations. More that they want it to feel authentic to the nostalgic memory they have in their head.
For example, games like Shovel Knight go for an 8bit style, but they're not limited to an 8 bit color space, NES sprite limitations, etc.
I get all that; I really enjoy the sound of some "imperfections" of old blues and jazz records, but I also don't consider any modern records which doesn't replicate those "imperfections" to be bad.
I'm not sure about Shovel Knight because I've never played it, but Mina the Hollower (also by Yacht Club) actually does conform to the those limitations. It's based on the art style of Zelda: Link's Awakening, and does so quite accurately.
Check out La Mulana.. the original version of the game conforms to the limitations of the MSX, but remakes do not. There’s plenty of room to do things either way!
It doesn't. I was using it as an example of it being done right, without actually following the limitations of the NES. But you can see from the article linked by one of the other replies the dev team put in a lot of effort to make it as close to authentic as possible.
But the real answer is they aren't inherently bad. People don't actually need it to conform to the past limitations. More that they want it to feel authentic to the nostalgic memory they have in their head.
For example, games like Shovel Knight go for an 8bit style, but they're not limited to an 8 bit color space, NES sprite limitations, etc.