To answer your question quickly and to the point, in recent times a small but vociferous collection of activist groups have unjustly singled out Charlie Chan as a supposed example of anti-Asian racial stereotyping. Anyone who knows even the slightest bit about Charlie Chan - an American icon - realizes, however, that this is about as far from reality as it gets!
Sadly, the movie networks are, during our "enlightened" era of political coerrectness, unwilling to risk incurring the rath of the above-mentioned groups. Can this unfortunate situation change? Of course, but it will take a steady banding together of Charlie chan fans to help bring this about. One bright spot may actually come in the form of Lucy Liu's planned "Charlie Chan" movie in which she, herself, will star as Charlie Chan's granddaughter. This picture, set at this time to be released in 2007, can, at the very least, get the name Charlie Chan back into the public consciousness, and, should that happen, who knows what may follow?
One thing that we can all do is try to contact the movie channels and request that they show Charlie Chan films. At our Bulletin Board page at this humble site, we have a link to the comment/request page for Turner Classic Movies (TCM), where you can take a few seconds and request your favorite Chan film.