People will choose free stuff over cheap stuff all the time. Study below has an experiment (experiment 2). They first offered people either a Hershey's kiss for 1ct or a Lindt truffle for 15ct. The majority took the truffle. Then they decreased the prices to 0ct and 14ct respectively, so the same price difference. The Hershey's kisses suddenly sold better than the truffle

https://web.mit.edu/ariely/www/MIT/Papers/zero.pdf

I dont know if it is mentioned in the paper, but one important thing is the friction of paying, even if it is 1 cent. It works the other way around too, sometimes people pay to avoid more friction in the future (like in those pay and you will get no ads, priority in the queue, etc, kind of services)

Free food just tastes better.