I cannot provide you with the reasoning or any ETA (nor confirmation if there’s any plans to add grid view to the Android mobile client).
All I can tell (and wanted to add) is that the grid schedule is not the only way to access the program guide https://support.plex.tv/articles/225877387-program-guide/
There exists a feature suggestion to add the grid schedule… but apparently this suggestion has yet to draw some attention (looks like not even the OP voted for it)
