I kinda agree with you on that.
A lot depends on where you start out.
I find folks who grow up bilingual tend to have an easier time picking up others languages as an adult.
I grew up as bilingual English/Spanish and as an adult picked up Mandarin, Thai and Lao, not the easiest as they are tonal, but I figured it out.
All my kids are multilingual, did the tried and trusted method of each parent only speaking one, but different language to them.
Now I would have to say, for whatever reason native English speakers seem to have the hardest time picking up languages. My ex wife could not master Spanish with me at all, and given the general age of expats in Thailand I'd postulate that difficulty gets worse the older you get, especially trying to learn a tonal language.
So I also say it's arrogant not to learn Thai, more a case of they probably simply cant. It gets harder to rewire the brain as we age!
On a nerdy note, and it may explain something about the aging brain, my two native languages float around in my head seamlessly, thoughts flipping from English to Spanish.
My learned language's don't work that way, I never 'think' in them and I constantly translate them in my head