refurbishing an old bike is like 8-10 hours of work.

at 50 dollars an hour that's 400-500 in cost of labor alone. parts will easily add another 200-300.

it is not economically feasible to refurb old bikes for sale. it's typically only done as charity work, or DIY project.

a new bike takes like an hour or two to assemble, and comes with all the parts.

even dumpster tier used bikes are usually sold at 200-400 dollar range at bike shops, and have very little profit unless they came in in pristine condition and just need a lube.

also they are far less safe and reliable than a new bike because you're using decades old technology. 70/80s bikes are deathtraps with horrible tires, horrible brakes, and very unreliable shifting. things dramatically improved in the late 90s and 2000s.