One of the main issues is the lack of competition. There are now only 3 main browser engines, Blink, Gecko and WebKit. Blink (which poses Chrome and Edge) is by far the largest, and has a the enormous marketing might of Google (and Microsoft to a lesser extent) behind it. WebKit runs Safari, which only runs on Apple platforms and arguably only has the market share it does is because Apple doesn’t allow other browser engines to run on iPhones and iPads. Gecko, the engine of Firefox, continues to slide into irrelevance (which pains me to say as a long time Firefox user).
We are in real danger of the web being trapped in a browser monoculture again, like the dark dark times of Internet Explorer’s dominance. This led to a period of stagnation in web technology Microsoft at the time put little effort into developing IE. Allowing Blink/Chrome to do the same will likely be just as damaging, albeit in different ways - particularly for privacy on the web.
For the good of the web no one company should ever be in the position to dictate web standards, which is why we need a healthy and competitive marketplace of web browsers and browser engines. The problem is that web standards have now become so complex developing an indecent browser engine is now a monumental task. Opera gave up on Presto, once the poster child for browser innovation. Microsoft, a company with far more resources, gave up on Trident. Mozilla was developing a new generation browser engine called Servo, but gave up on the project also.