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.