Why not? Maybe they think that people who can do well in the college entrance examination have strong self-control ability and stable working ability.

Although it is not 100%, people with regular undergraduate background are good children at school, so they are better educated.

People outside are in a mess, good and bad. The unit is unwilling to take risks because it can't be recognized at a glance.

It's easier for you to understand from the standpoint of the unit. Their big companies just don't want to take risks.