I think the key issue for the UK and US was the idea of "herd immunity" meshed quite well with the prevailing ideology of their leaders. BJ and Trump were loath to shut down the economy and limit the perceived "God Given" rights to freedom of movement and "exceptionalism". The only thing exceptional about those countries now is the mortality rate.
Thailand had no such problems. Once they saw how the Chinese dealt with it and the disaster unfurling in the West, they shut it down.