It exists. It's called android! Honestly though, that's why Google developed it. They wanted to maintain control and stay as the primary Internet portal for mobile users. Banking, messaging, gaming and productivity all passes through them.

We chat has similar in China but only because competitors were stifled. It won't work in the west as competition for any aspect will be better for some people and anticompetitive behavior will be clamped down on even if it started to work.