In fairness to the players, this is, at least in part, due to the fact that pro players in America have fallen on tough financial times and have less self-esteem than they once had. Dressing formally or semi-formally is expensive and, in my view, unnecessary, but dressing presentably is inexpensive. I also feel that poor dress today often evidences diminished respect and a lack of accountability to event producers/promoters.
The PBT is often looked upon as "the bad old days" on this forum because most prefer to focus on the indiscretions of Don Mackey and ultimate implosion of that tour, but those were the "good old days" in terms of making money. In 1998, there were sixteen events having $100,000 added each. Players were making money and the way they presented themselves reflected it. Two players in particular, Kim Davenport and Jim Rempe, dressed impeccably, and quite a few followed in their footsteps.
That said, quite a few top American players dress nicely today. Johnny Archer and Jeremy Sossei are good examples. Of the younger players, I'd call Justin Bergman one of the classiest dressers.
In the end, however, if there is no dress code, as is often the case in events played in America, we must accept that players will dress as they choose. If the self-esteem of American pros improves, it will bode well for how the players present themselves, but like JohnnyT, I hope they will choose to present themselves more professionally sooner rather than later because their image is at stake.