The sales of most professional sports teams are fairly predictable.

They happen because owners die or cannot figure out how to pass the team on to their families. They run out of money, are more focused on other pursuits or are pushed out because of misconduct.

Once the decision to sell is made, the process plays out in a relatively public way. Bankers are hired, potential purchasers register interest, an auction occurs, and weeks or months of reports in the news media follow.

So it was a complete surprise last month when, with no warning, the families that control the Las Vegas Sands casino empire announced that they had reached a binding agreement to buy a controlling interest in the National Basketball Association’s Dallas Mavericks from Mark Cuban. The only thing that made sense was that the situation involved Mr. Cuban, who has long run the Mavericks in an unconventional manner.

Still, more than two weeks later, the basic question surrounding the sale — Why did Mr. Cuban do it? — remains mostly unanswered. The reliably loquacious Mr. Cuban, who always seemed to be having more fun than any other owner, declined to speak on the record for this article. The Adelson and Dumont families, wary of getting ahead of an N.B.A. approval process that includes due diligence and a vote on the sale by other team owners, declined to comment beyond a statement expressing their excitement.

But what is clear is that the sale represents a window into the rapidly changing nature of the business of sports.

When Mr. Cuban bought the Mavericks in 2000, flush with cash from selling Broadcast.com just before the dot-com bubble popped, professional sports teams were still mainly just teams.