No, the problem is that people can sue (and win!) if they eat food from a company’s garbage bins and then get sick. Remove the liability, and you remove the motive to protect against said liability at the expense of the commons.

Hmm, I can't find (in one minute searching, busy, sorry) someone winning such a case..

I find it a bit strange. First, because many people do dumpster diving. Second, because it is mostly the big companies locking their bins, so why do the smaller ones don't if it's risky?