There doesn’t appear to be any sort of popular socially conservative party in Thailand:

The Marriage Equality Bill, which saw multiple versions proposed by the ruling and opposition parties as well as through a public petition, received resounding support in the House of Representatives. As many as 369 MPs voted in favor of it versus 10 who voted against the proposed legislation.

In spite of:

A recent survey by the Pew Research Center, an American think-tank, revealed that 60% of Thai adults support the legalization of same-sex marriage. This places Thailand behind only Japan (68%) and Vietnam (65%) in terms of support for such a measure in Asia.

Which means there is some serious squashing of public sentiment going on that we do not see somewhere in the field of 30-40% of legislators opposing it.