It's not as simple as you're suggesting. With Closure you sometimes have to rewrite otherwise correct and idiomatic JavaScript significantly to avoid it breaking during compilation.
If you design your app to use Closure from the start, it's not a problem at all, and as a sibling comment said, CLJS apps get it mostly for free.
The entire JS toolchain lost five to ten years by not adopting Closure. I suspect that in a year or two, someone will release a webpack plugin that does the exact same thing Closure did, with the exact same constraints.
