To support MU-MIMO / beamforming (multipath signals for multiple devices) they could also just add more flat surfaces inside the ceilings to make radio reflections/echoes less complex so that the signal processing doesn’t get overwhelmed when the source is some distance away.

Plain absorbing material removes interference but doesn’t let you use MIMO tech as effectively, because the newer higher end routers can use those reflections to boost the signal

https://www.analog.com/en/resources/analog-dialogue/articles/massive-mimo-and-beamforming-the-signal-processing-behind-the-5g-buzzwords.html

I thought of interference too. If the Wi-fi was bouncing all over, there may be many areas with destructive interference – weak or no Wi-fi.