[Avaboormavoro]

I believe that if the marriage is not registered then there are no legal guidelines for the division of assets because as far as the law and/or government is concerned the couple was never married.

Also, I'd like to take the liberty of trying to answer your second question, however not being a Thai myself, my answer can only be taken as observation or speculation.
Perhaps they feel that a marriage has nothing to do with the authorities and everything to do with themselves, their families and Buddha. Even though many couples choose to have the ceremony without going down to the ampur, in their eyes and in the eyes of their families and all the people in their village, they are certainly married. I think that people may think that registering the marriage is just a lot of meaningless red-tape.

In fact, my wife and I registered our marriage 18 months before we had the ceremony and in the eyes of her family we were not married until we had the ceremony. Actually my wife also thinks that as well. So while I like to think that we have been married for 2 years, she considers us married for only 6 months