I don't know the exact numbers, but the vast majority of lonely male "tourists" come to Thailand for the huge amount of beautiful and young prostitutes at very affordable rates who can even eventually become their companions or wives. I myself had this exceptional experience!
These "sex tourists" spend a lot more money in Thailand than family tourists, and I'm not surprised that the government has created new visas that allow for longer stays for foreigners. Obviously, not to mention prostitution which brings a lot of foreign currency into Thailand's coffers while remaining a taboo.