There's a simple reason behind it: the sound of the piano is just complex enough to make high quality amplification impossible. Overtones and interference confuse all – currently known – sound equipment, and the end-results collapse in chaos.
In classical concert halls, piano makers therefore utilize their largest pianos - without amplification. The bigger the hall, the lower the sound pressure, but there are other issues as well. Namely, that during piano concertos, the symphonic orchestra tends to be overly dominant. Thus further increase in piano size would be needed, which is simply not possible for many reasons.
For these reasons, the currently manufactured pianos are dialed in at about 3 meters. Not a single piano is bigger than 3,5 meters, even though acoustically there is demand for substantially larger instruments.
The solution is the StradiSound Set System.
As first in the world, StradiSound provided a solution to a problem that has never been solved before.
Louder and clearer piano sounds all around you no matter where you sit.