What is the reason for Analog Beam Forming in > 6 Ghz?

Hello Experts,
What is the reason for Analog Beam Forming in > 6 Ghz?
Why not Digital BF?
What are the limitations?

It is difficult in mmwave to implement a high number of tx/rx chains for analog beamforming.
This is why in mmwave mimo is mostly 2x2.

Thanks @rf_5g, it’s logical. :wink: