@Bruce ********
Very easy answer. Many people are not interested in learning a very hard language (I'm learning myself and after I speak 3 other languages Thai is crazy hard in many ways. And I'm not even talking about reading and writing, that's a different story. )
If you are not living in the rural part of the country where very few people can speak English, you can get very far with English. 99% of them live in areas that are full of expats and other long-term foreign people. So they can communicate in English/ their own language. So no much need to speak Thai.
A big part of the long-term foreign are old expats. I don't know because I'm only 40. But I guess when you are 60-70+, you have a really small motivation to learn a very hard, new language when you can live a comfortable life without it.
For me is easy. I always learning the language of the country where I'm living. I'm learning basic phrases in every country I'm visiting because I feel better myself if at least I can say Hello, Thank you, This is good, Very tasty, etc. in a local language. For me an extra motivation is my partner is Thai and her parents don't speak any English (They even speak Isaan, just to make my life more fun/harder π€£ ) So I want to be able to speak with them even on a very basic level, but more than Hello and How are you. (I can do that already)
So before you start judging people, just think a little bit. Everyone has a different reason. Even if that's just laziness, an "I don't care attitude" is still their decision.