For a long time, states were able to control the practice of law within their boundaries. There were occasional border incursions when state regulations limited what lawyers from other states could do. In general, though, it worked. The e-world changed everything. The Internet requires a new approach to lawyer advertising and to geographic limitations on lawyers' practice.
Regulation needs to be uniform throughout the country.
It used to be inconvenient to communicate with someone two states away. It was difficult, or at least inefficient, even to find out what the law was two states away. And a potential client had no easy way to find you. The Internet enables you to easily touch people everywhere. If communication and knowledge are the lifeblood of lawyering, then the Internet is communication and knowledge on steroids.