It just looks clean. Lowpoly games benefit from running at high resolutions to a surprising degree. The better the art, the more it benefits from being shown with as little obfuscation as possible. There are texture packs and shaders available for popular old games, but even without them, it's often worth it to ramp up the resolution, even far beyond 4K. I've played some old games at ridiculous resolutions like 5k or more, eliminating even a hint of jagged edges. You can then add a touch of retro flair through scanline and bloom shaders.