Hi Jennifer,
I have been crossdressing since age 5, and now 66, and in the last year I have really worked hard to answer your question for myself. The best scientific answer I can give right now is that crossdressing is our chosen means to a satisfy a need, and that need can vary in complexity at any moment. We may want to look beautiful, or to explore what that slip might feel like, or to fantasize about sex, or to submit to a fetishistic impulse, to feel light on our feet, or to escape the stresses of manhood as we feel them, to be unique, to try to reach in and inhabit a world we imagine is found for those who wear such and such clothes and have such and such look, etc..
The pinkness -intensity of our desire correlates to the intensity of the need, and the fogginess increases with level of tension, frustration, confusion, or mystery that is involved with the need.
Listening to others here, and I feel it too- sometimes I just reach for some pretty and light bikini panties in the morning, and peacefully underdress to be able to remember my feminine side all day, and support it, and , and my day is better and more peaceful. It works, for a while. Then I see a lingerie ad and am overcome by jealousy and desire to be on the receiving end of the kind of attention I am paying to the model. Or I am just angry that people are discriminating against LGBTQetc and I want to go out all girly just to stand up for our gang and say that gender norms are arbitrary. I often just feel bored and drab and pedestrian and I want to feel light and perky and eye-catching. Or I wish my wife would reach for me sexually, which gets translated in my wiring to wanting to dress in a feminine way. Crossdressing is an attempt to satisfy all these needs, and it works 100% only in my anticipating imagination.
Once in a while some of these needs may evaporate, and if they do, I won't want to crossdress to satisfy them. I am hoping to find a different way to satisfy some of them, as another means to reducing the stress that crossdressing causes in my life. So far I can get a lot of needs met by wearing a borderline feminine top and artistic jewelry. I"ve tried to be noble and forgo crossdressing, out of trying to make life better for others who don't like it, but the mass of needs tangled up with crossdressing make that unworkable over any long term.
Crossdressing is an effective shortcut to all sorts of emotional relief, and there are no other solutions that can compete with it for speed and effectiveness, at least in terms of emotional satisfaction. That is why we seize on it so strongly when the opportunity arises in our lives. Of course, it is not generally accepted or condoned, yet, by the society that creates the need in the first place by stultifying the emotional growth and balanced identity within boys and girls.
So we soldier on and try to make best use of it without causing other problems to multiply.