Why is TV show QI shown at a specific time?

Question

Doing some research about TV shows and how they are shown at specific times on specific channels. QI is shown on BBC2 at 10pm on Fridays, but I don't understand why it is not shown at prime time between 7-9pm when many people are watching TV? thanks :)

Answer 1

the Watershed -- Q.I. often has sexual jokes( the penis often gets mentioned)

and can have more mature content