Geza Vermes explores the issue in the Guardian:
Christianity has not always been a religion so preoccupied with sexual behaviour (or gender identity). Theology used to challenge ideas; people's behaviour in bed did not rank among its top concerns. Consider the arguments which raged at the time of the Reformation. The reformers and counter-reformers aimed much higher than their latter-day heirs and focused on the ultimate source or sources of the Christian faith. Was it scripture alone or scripture and tradition or ultimately the magisterium, the Christ-given doctrinal authority of the church?
It is a curious shift, and for whatever reason Christianity today appears to be very much obsessed with sex and sexual matters: who's sleeping with whom and how and when and why. Are all of the really "big" issues settled, leaving nothing else for people to talk about? That hardly seems likely.