Same reason that not every business in America has been forced to comply with the ADA (Americans With Disabilities Act). We don't have enough lawyers.
It's just a matter of time, though. There are more lawyers in law school than there are practicing law today.
That's a mighty discouraging thought. I think we have some 600,000 practicing lawyers the last time that I looked, and over 2,000,000 people employed in the legal area.
Ballooning that already too-large number further is just an impediment as far as I am concerned.