1)Why are there so many trancegender people in Thailand?
There are many transgender people in Thailand, but I think it doesn't mean "People in Thailand tend to be transgender." Maybe, this is the reason why they are Mahayana Buddhist. They tend to believe "Samasara(the transmigration of the soul)." Therefore, they think transgender people are influenced by their previous existance, and they have the culture that accept transgender.
So, transgender people in other countries are probably as well as Thailand. However, almost all people in other countries don't have the culture like that of Thailand. They are perhaps influenced by their religion a little.
It doesn't mean Thailand has especially many transgender people.
2)What do you think about to transgender people and their several rights?
Transgender people are not so different from us. Certainly their sex and gender are not same, but they don't harm to other people. We should admit this is their character. So people have to give social rights for them just like us.