The culture has not shifted. The politicians have. Note that all the “gay marriage” push comes from the top, primarily from activist judges. The most egregious, the Prop 8 debacle, came from an openly-biased judge (gay) who was not qualified to make the ruling.
Four states have enacted gay marriage by a vote of the people. Many more have enacted it by votes of the Legislature which were not followed by those legislators being voted out of office.
Yes, many states still resist gay marriage and have it only as a result of judicial decisions. But there is clearly a lot more popular support for gay marriage than there was a few years ago. If you don't see a cultural shift, you're not looking very hard.