In the early days when China opened up, their citizens were very keen to learn English. They took every opportunity to practice the language with tourists visiting China.
In 1990s, there was an influx of workers from China to Singapore. In those days, semiconductor sector had a large number of China citizens in their workforce (we don't refer to them as PRC then). Many of them were graduates. Those from university recognized by Singapore held senior positions, while those whose education certificates were not recognized, worked as production specialists (something like production operators). Thus, even the lower rank work force was highly qualified.
They spoke Mandarin which though accented, but could be easily understood as they were mainly from Beijing and Shanghai. Communication in English was not an issue. Though they spoke amongst themselves in their native tongue or Mandarin, but to us locals they were willing to communicate in English. There was never a problem of them telling us off that being Chinese, we should speak to them in Mandarin.
Fast forward to present time, PRC now demand that we locals communicate to them in Mandarin. Sigh! Their Mandarin is so heavily accented it sounds foreign instead of familiar. There is a larger influx of workers from PRC and they are not as qualify as those in the 1990s. They compete with lower income workers for jobs. They worked in cleaning, food, sales and transport industries.
Besides their poor mastery of English, they are an arrogant lot too. There is a possibility that even though some could communicate in English, they refuse to do so. China is a big brother now, so their citizens are acting 'tough' to show their national pride. Perhaps they feel ashamed that their standard of English is lower than local Chinese. To hide their shame, they become demanding and aggressive to locals.
My mum who is educated in Chinese till only primary level, understands English well. She can speak in English (more to Singlish) to get through any daily activities and hold a conversation even with a native English speaker.
The point is, PRC could handle English if they choose too. But likely they don't see the need to do so. They are here to invade and conquer.