English not only language of importance in Thailand

Dirk Sumter writes that Thailand desperately needs an English-speaking workforce. 
May I ask why? 
I do have my moments of frustration communicating with Thais in the service industry, but I also acknowledge that I have a commitment to learn and understand the language, even if just the basics. Thais I meet are very grateful for the effort. 
So then, why just English? What about Mandarin or Cantonese for the hordes from mainland China who refuse to speak any language but their own. 
What about obscure dialects from the ungrateful Australian suburbanites that even I, as an Australian, have difficulty understanding. 
So, too, the Texan drawl, the Cockney jibberish, and the machine-gun rattle of Italian and French backpackers? 
I, too, had a multilingual upbringing amid the Ukrainian, Romanian, Polish, Hungarian and Czechoslovakian tongues of my parent’s friends who came to Australia at the end of World War II.
Why place it solely on the shoulders of the already burdened Thai workforce? 
Leon Dimitresku