The Daily show touched on this subject last night and had a great interview with two retired transgender US Army veterans (one that was the first to receive France's highest military honour since WW2).
Its reported that the decision comes because Trump is trying to find funding for his fecking wall believe it or not
The figures they gave were that the largest saving on Transgender medical costs alone is an estimated $8.4m per annum (this is 0.001% of the total projected US military spend).
Meanwhile, costs for the Trump family spending time at his New York City and Palm Beach resorts (money that goes to companies in his name) is this year $60m alone.
Go figure!