I believe the wedding industry in Japan filled a niche (and a quite profitable one at that) in providing the romantic, western type of wedding that Japanese females see on TV and in the movies. I believe the wedding of the late Princess Diana had a lot to do with starting this "custom" in 1981 as most Japanese females I spoke to at the time remarked on how beautiful and romantic it was and that they'd like to have one like that.
It could also have started when singers and talento and such started having christian style weddings during that period as I don't remember hearing of christian type weddings before that (although they could well have existed and I just wasn't aware of it).
Some people above have stated how hypocritical and "disgusting" it is, but I see no harm in it as I have seen numerous weddings here in the US where the couple gets married in a church but hardly ever sets foot in one afterwards. They claim to be Christians, but they never practice it. Isn't that disgusting and hypocritical also?
As nice gaijin stated above, "Shinto, Buddhist, Christian, or Secular, wedding ceremonies are purely for the indulgence of the couple and their guests" and are nothing more IMO.
In my own case we had a Shinto wedding with the complete ceremony in kimono and all along with the tux and white wedding dress as that is what the parents wanted. As they were paying for it, who was I to argue? It made them happy and that's all that mattered in the end. If it was up to me and my wife, we'd have preferred the city hall and a nice honeymoon and saved a boatload of money.
I wonder how women feel, especially Japanese women. Do they want all the pomp and ceremony of a western style, Christian wedding as it's romantic and the "in" thing to do? Or, do they do it to impress their friends and are just copying celebrities?