Other commenters are criticizing details, but I really appreciate the OP trying to see the entire landscape. I agree with other commenters that ownership over

Other commenters are criticizing details, but I really appreciate the OP trying to see the entire landscape. I agree with other commenters that ownership over code is a primary driver (at least for CSS style vs. javascript interaction). Leaving aside details, it seems clear the javascript frameworks were ahead of the platform and had the perverse incentive of staying that way, which also took the pressure off browser developers (already slowed by inter/standards politics), resulting in a long historical period of dissonance. By comparison, Java bytecode gave Scala and Kotlin instant access to the enterprise, and the JDK team responded with faster cycles and steady but measured incorporation of features, because they realized they needed something to get enterprise off Java 1.8 and into licensable VM's. Progress is slower in the enterprise, but the dissonance seems minimal.