Who cares ...
Those Thais fluent in English rarely use it. All are taught now, and most understand it, but simply don't use it. TBH, have no use for it, unless in the tourism trade.
I was pretty good in Spanish, French & Latin (of all things), and forgot almost all of it. If watching a movie, and Spanish is spoken, I barely understand most of it. Catch a bit, but that's all.
I live here, and can't hold a conversation in Thai, and don't need to. Just as most Thai, don't care to use, or even need to know English.
For financial gain, workplace, Chinese is more useful to know.