"The ability to be fluent in many languages is a valuable skill ... for a headwaiter"
-- Otto Von Bismark, German Chancellor
There isn't much point in learning to speak barely passable Mandarin Chinese when everyone in China speaks the Lingua Franca ... English.
everyone doesn't
Everyone with whom a foreigner might be dealing. China is a country where you could live for a decade and never learn more than a few words because you don't need to speak Mandarin to do your daily chores.
In Korea or Japan ......
That would be true in any of those three countries if you stayed in the big cities, but untrue in all of those countries outside the major metropolitan areas.
I lived in Seoul for five years, in two different Ku in Tokyo for six years. I spent six years in Hong Kong (before and after the handover) while a frequent visitor to Guangzhou and Beijing. That's based on my personal experience.
At work, I spoke only English the entire time. In Hong Kong and China, taxi drivers seemed to be the exception to the 'everyone speaks English rule'. But, as long as you can say your destination in passable Cantonese or Mandarin, it seemed to work. Same for Japan and Korea, English was all I ever needed at work. However, shopping, transport, and everyday errands required me to speak local. Singapore, I never heard a single soul speaking anything but English if he was wearing a clean shirt.