Why do people purposely sabotage heists?

Had a guy during the apartment heist convoy setup mission who decided to take the truck to the other side of the map and fuck around. We had to just blow him up in the end failing the mission.

Just had a guy in the in prison break station setup who constantly rammed into me in his vigilante right at the end of the mission so I got out my car, so he decided to flatten me twice so I just left at the restart screen. Felt sorry for the host but I can't be bothered with these idiots.

Anyone else experience this shithousery?