That's exactly the point for Uber: they lost against a local company, because the government did everything it could do so that didi would win the battle.
I've used both Didi and Uber in China many many times, and it seemed like they were competing against each other pretty hard, without discounts etc.
From my perspective as a customer, it seemed like they were both just trying to outspend each other to gain market share, and Uber just decided it was no longer a good use of cash.
WhatsApp never entered into China market, never register as a company in China, so how it could follow the regulation?