re: Why have churches started allowing gay preachers?

It started on the early 1900's. Go read about Harry F. Ward, a Methodist minister and theological seminary professor. He was an open communist and a founder of the Federal Council of Churches. He spent time in Russia and was good friends with Lenin. Not only was he in the FCC but he was the ACLU's first chairman. Later he resigned when the ACLU pretended to kick out communists.

In 1950, the FCC merged with other groups to form the National Council of Churches (NCC), but their communist agenda did not cease. In the 1960's the NCC released several screeds calling for the U.S. to embrace communist China, leave Vietnam alone, and to officially recognize Castro and Cuba. The NCC funnelled money into various communist countries which was used by those regimes for their own purposes. Before 1991, the NCC parroted the Soviet line completely. They never once criticized the Soviets but routinely bashed America.

Today the NCC is still around and especially influential in mainline Protestant churches. If you go to their website, it is nothing but lectures on environmental Justice, how evil whites are, how trans people are wonderful, and how America needs unlimited immigration.

To answer your question: Churches have went crazy because the communist left has worked for decades to get "their people" in leadership positions.