Because lines are marketing/publicity/advertising. The longer the line, the more effective your publicity is, and the more long-term popularity you are stacking

Because lines are marketing/publicity/advertising. The longer the line, the more effective your publicity is, and the more long-term popularity you are stacking up. It's probably a short-term profit to have the restaurant charge more and to have shorter lines, at the expense of foregoing the free/best publicity possible long-term.