UL data rate is less because
1. UL prb allocation for pusch is less compare to DL pdsch allocation. In UL , ue need to have prb for pucch and rach .
2. In UL , ue transmit from one antenna only but in DL can receive from 2 antenna.
3. In UL 16/64 qam modulation is used while in DL 64/256 qam can be used.