Well, I could be flippant ...
...and just paraphrase comedian Chris Rock's famous quote that "a man is only as faithful as his opportunities", substituting the word "crossdresser" for "faithful". That's certainly true for many of us here, once the genie has been let out of the bottle.
But it is also safe to say that stress has a lot to do with it, and that our urges to dress up will often coincide with the amount of stress that we may be under at any given time. It is well known that there is a strong correlation between the two, but the good news is that unlike taking drugs, alcohol or binge eating for the same purpose, crossdressing in itself is not as self-destructive, nor is it fattening ;).