Theoretically, the bride is busting it out for her groom. She's showing off what he's getting, and he's supposed to be proud of her like that, etc. I do get your point though, and I personally disapprove of too- revealing wedding gowns, I think they're in poor taste. If they must be revealing at the reception, at least wear a cover up in church, right?
It wasnt always that way. Never were strapless dresses worn. I am heartened to see more and more non strapless in the brides magazines.
Maybe they think it looks good on them.
You'd have to ask a bride showing a lot of cleavage. I know that a friend of mine (soon getting married) is a bit larger and, as such, has quite a large bust. Dresses that don't show off any cleavage at all make her bust look HUGE so she has always steered towards a little bit of skin to make her look more in proportion.
maybe they think theyre supposed to