They're pretty important for this free online graphing calculator (widely used by high school students and teachers and even starting to be used on some standar

They're pretty important for this free online graphing calculator (widely used by high school students and teachers and even starting to be used on some standardized tests): http://desmos.com/c http://desmos.com/c There is also some niche use as a component of sandboxing: https://gist.github.com/pfrazee/8949363 https://gist.github.com/pfrazee/8949363 Your point is well-made though. Very few kinds of webapps are CPU-bound, graphing calculators being notable as an exception (and even then, Desmos made do with the main thread before Web Workers were usable). And while lots of webapps could use plugins, browsers could provide an API for sandboxing code that runs in the main thread, or with a GIL. The reality is, though, the cat is out of the bag. WHATWG is committed to making the Web into a fully-featured platform for WORA apps with all the same capabilities as a desktop app, and multithreading is one of those capabilities. Even if the next Spectre/Meltdown dooms Web Workers in their current incarnation, browsers will run workers in Docker containers if they have to.