why base stations have 2 receiving antenna and only one transmitter?
'Of the three antennas, two are for receiving and one is for transmitting. Two are used on the receive side so that the base station can compare signals and select the best antenna for each user within the cell. This is known as 'diversity' reception to more equally manage the power differences between the cellular base station transmitter and the small battery powered cellphone transmitter.'

Reference:

https://ethw.org/Cellular_Base_Stations