Because your body is like "oh, I don't need to retain any water.. I'm receiving sufficient supply now" instead of "oh sh*t, we aren't getting much water... better retain some of it just in case."
Possibly?
I too wish a treatment would come out that could stop hairloss permanently. However, you have to realize there are a lot more important things that the money and time could go into. Things like AIDS, cancer, and other diseases that aren't primarily cosmetic (like hairloss).
So when my hair falls out, sometimes it has a little thing on the end. Some of these 'things' are balls of whitish-yellowish grease-looking material. I'm guessing this is DHT buildup?
Also, some of the hair falling out has thin white 'casings' around the end instead of those balls.
My hair...
Just to chip in... I was on finasteride for just a few days but then get off, as I realized it was changing my hormones on a noticeable level. I started to gain weight, especially in my face. Whether that was fat or estrogen, I'm not sure.
I also want to say that a lot of people defend the treatment...
The dermatologist didn't really even look at my hair, she just gave me a prescription and a month's worth of samples for Propecia. She was also really pushy about getting a couple moles removed. Worthless doctor.
I think some people just 'react' more to increased estrogen than others. I too had signs of heightened estrogen levels.
Also, the thing with hormones affecting you immediately... it wouldn't necessarily have to occur this way. There might be something that becomes worse and worse as time...