For various Asian nations, the time spent under colonial rule was one of transformation. While there were many positive outcomes from this period such as new infrastructure and industry, it also led to the decimation of various liberties, industries and communities. In particular, it also led to a dilution of culture within each nation for that space in time where there was sometimes irrevocable change taking place.
When it comes to Thailand however, the story is a little different. This nation remains the only Southeast Asian nation to maintain its independence throughout the period of Western colonization and thus has been able to retain its cultural identity without any influence of foreign entities.
This is what has allowed Bangkok to become a nation with cultural norms that are much more liberal than its other Asian counterparts in many ways.