In satellite technology why uplink frequency is more compared to downlink frequency.?

Answer 1

You can send more information, more rapidly on a higher frequency.

Answer 2

The idea is that the higher frequencies will be a little more reliable than the lower, and if you get a fade, they want you to lose the downlink first, so you won't keep transmitting. If you lost the uplink first, but kept transmitting because you didn't know it, the satellite wouldn't know you were transmitting and would clear other earth units to send on that same channel.