The more LGBT people are accepted in society the more likely it is for people to come out of the closet. Simple as that.
Most likely there were always as many LGBT people as there are now you just see them more now because we feel more comfortable coming out and awareness helps people realize what their feelings and thoughts mean.
Edit: oh and nobody is “going” trans they always were if they are, they just might not have realised it yet.
The most common reason for trans folk to detransition is that they encounter to much bigotry, hate and generally receive no support from their family/friends and/or the people they love.