[sansnomme]

Unlike Erlang/Go/certain Clojure libs, the JavaScript flavor of async is primarily around red-blue functions. A lot of stuff is explicit and not handled by the runtime. A single async keyword can easily taint the entire codebase.

See: https://news.ycombinator.com/item?id=8984648

More importantly, frontend is extremely demanding in terms of UI. While for e.g. QT, WxWidgets, native GUI toolkits, it is perfectly acceptable for things to look the same. On the modern web, every significant app is expected to have a "design language" and not look like each other. On the other hand, HTML by default isn't very stateful, sure it has some stateful components like checkboxes but in general you have to store the state in code. And every code base needs a custom UI. You end up with a state space explosion. That is also why frontend frameworks these days are trying to force things into finite state machines i.e. Redux, Elm architecture. Whatever term you prefer. Half of your UI codebase often have absolutely nothing to do with business logic and instead animations and user experience code to make things feel "slick". A ASP.NET WebForms just ain't going to cut it if you wanna build a SaaS. Sad because tons of money have been wasted on essentially marginal improvements on user experience, but good if you are the consumer of course.