on a retro forum, taking a low-end early frameset & choosing to use entry level bits rather than opting for better components to give a project a true entry level factory spec takes a certain amount of dedication.
To actually build and then ride a bike built with low end kit, on a low end frame for the sheer enjoyment of the lack of precision & finesse is, in my opinion, cool!
I agree with the first point, it does take dedication, but so does any obsessive hobby even collecting old bottles or cans. Dedication to something still doesn't make it cool.
Do these people build the bike that way because it's what they've always wanted or just to be different?
'cool' is ultimately decided by the way an individual views it.
to compare groupsets to engines in cars... a rusty 1.2 litre mk1 escort thats been left in a garage for the last 20 years isn't cool BUT if someone puts in the hours to do a full resotration and painstakingly refurishes every part, rebuilds the car and enjoys driving it every other weekend at his local owners club when the suns out. the engine itself isn't cool, the context in which the engine is used is cooler than a polar bears toenails to those who move in similar circles. to a chav who looks like he glued an oversized airfix kit onto his corsa, that guy driving around in a 20 year old car is uncool.
from what I can see, the cool wall votes seem to be looked at in black and white by a lot. take something we deem to be 'cool' out of context and it looks daft, regardless of how cool it may be in the retrobike (or wider MTB) community. take something uncool (like low end groups) and put them in the right context and their coolness grows substantially... at least in my opinion it does anyway!