Ubers not taking 4 people

Just yesterday I was trying to book an uber for 4 people. But 2 Ubers refused to stop for me because they said they’re only taking 3 and not 4 people? So we had to order 2 separate ubers. One uber said its because of COVID and another says demand (makes no sense). Can someone explain to me what exactly the reason is as to why they won’t take 4 people?

Bare in mind UberX seats 4.