I've pulled complete, easily repairable bikes from seasonal bike store dumpsters. Such stores want to sell bikes. Period. End of sentence. They don't want to do complex repairs or even patch tubes, so what they throw away is choice.
The bike they took in trade to make a sale?
Dumpster.
The more-than-a-tuneup-needed older bike?
Dumpster (owner heard what the repairs would cost him, and when revived, bought a new one).
They really just want to make as many sales as possible before ski season.