Most of these "new retro" games are coded with modern tools and engines, they often only approximate the look and feel of retro games (their code is very modern and much easier to deal with) and the restrictions are broken as soon as it is too inconvenient. They can be great games, look nice and be congruent with their inspirations of course, but the ones built with real restrictions, be it actually made to run on real retro hardware or some kind of fictional VM like in UFO 50 or attempting to recreate a similar graphics system like the NES PPU tiling and pixel restrictions in Shovel Knight are much rarer and take way more effort to make.