Why did Nikon choose 36 megapixels ? - why not larger ?

Why 36, because it was because after much research and drawing trend lines and industrial data gathering they knew they would be head and heels more pixels than Canon and all the fanbois here would feel much more secure in the equipment.

Of course things like how many pixels one really needs to actualy produce stunning pictures isn't important, how good your lenses have to be to resolve, how limited your aperture range will be, how precise your focus were not as important as just having the most pixels!

Technology will march on, there is nothing stopping higher pixels, finer lenses, more precise focus, faster processing to enable making up for loss of light for them smaller pixels.  The bigger challenge will be economic.  As long as the fanbois feel that having the most pixels is important and will blindly throw the money at it, the lenses etc. etc. then nothing will stop it till the economics doesn't make sense.

This has nothing to do with athletics buddie, its technology and that is all about money and ROI.