You are right, and wrong. Most people do prefer to stay where they are, out of habit.
It's not a peculiar mindset. Different, yes. I would die of boredom in Australia.
I speak Thai quite competently.
Thailand probably has the best infrastructure of any SE Asian country, except Singapore.
Many retirees here have Thai families they support, and get support in return. Your "sad and lonely" retirees occupy bar stools, I doubt they are a majority, albeit most visible.