I heard a news that Thailand became the first Southeast Asian country to legalize the same sex marriage. Taiwan was first in Asia to legalize the same sex marriage in 2019. In the world Netherland was the first country to legalize it in 2001, followed by Belgium(2003), Canada, Spain (2005), Norway, Sweden (2009). Most of them are Western countries. The UK and US legalized it in 2014 and 2015, respectively.
Religion appears to be a major factor for country to decide if same sex marriage is legalized. But conservative Catholic countries such as France and Brazil have already legalized it. In contrast it is still illegal in most Asian countries. I think Asians are relatively conservative and not proactive to innovating.
In light of evolution of animal's life, it is natural for human being to feel uncomfortable about the same sex marriage. I think that in European nations freedom of individual is prioritized over human nature. In other example of individualism in Western countries separate surname for husband and wife has been long legalized in the US and UK, while it is still illegal in Japan.