Why from the 32/64TRX antenna elements we can have only 2/4/8Rx receivers?

What is the reason why despite the fact that gNBs have 32 or 64 TRX antenna elements, at the end we are able to use only 2, 4 or 8 Rx antennas for receiving in UL?

32 or 64 TRX antennas are about numbers of physical antennas which used for beamforming

2,4,8 Rx I think refers to number Rx FR chains which are capable for Rx diversity.
Just my assumption