Airlines already do that for business routes. Just in the other direction on pricing. Pre-Covid there were a couple airlines playing around with business clas

Airlines already do that for business routes. Just in the other direction on pricing. Pre-Covid there were a couple airlines playing around with business class only flights from NY to LA. Solo business travelers are where the money is made. The rest of the seats tend to exist at cost or even below to fill up the plane. Airlines would be pretty foolish to try to lower margin on the least price sensitive class of traveler they service.