I think that you'll find that it gets back to a legal issue.
Owners / Operators / AOC holders for all aircraft are required to keep amendments promptly up to date for all POH's. There would be no control of amendment status of the POH if it were privately available 'off the net' or from some other unofficial source.
I do operate in a company where all of the pilot issued manuals are E-manuals, but there is strict control within the company to ensure that each and every pilot has the 'up to date' manual before operations. Even then, reminders abound within the manuals that their information is not the official operating manuals for the aircraft, the originals may only be found in the aircraft.
It IS an excellent idea, with very difficult 'policing' problems.
Regards,
Old Smokey