Hi Penelope,
Guys that post photos with other girls on their dating profiles want to send the message that they have dating options.
They want you to know that other girls desire them and you would be doing yourself a disservice if you were to swipe away.
Guys like this believe that women become inherently competitive when they see a guy with other girls. Such women get the urge to win that guy’s attention over said girls.
In posting photos of himself with different girls, he is hoping to spark that sense of competition in you and force you to chase him.