It really is hard to find non-strapless dresses lately. And that is a problem when the wedding is to be held at a house of worship or other venue where strapless clothes are inappropriate any time. My daughter-in-law chose a strapless wedding gown and spaghetti-strap-optional bridesmaid dresses. The attendants all had to wear some kind of little lacy shawl, and the bride wore a tiny bolero, for the ceremony at the synagogue. It looked okay, but I was sorry they had to spend the extra.
The synagogue doesn't have a RULE about this, but it's not considered in good taste for women to attend services or ceremonies like weddings with bare shoulders, any time. Guests bring a wrap of some kind. And I have to admit that when brides wear strapless gowns with no covering for the ceremony there, it just looks a little wrong. Like if a man weren't wearing a head covering in the synagogue. No one says anything, but it seems like she just was ignorant of what is considered appropriate for the venue.