C and even C++ run in far more places than Javascript does or ever will. People using other languages won't be interested in or able to use your library written in Javascript.
Anyway, I don't particularly care about writing code that runs on every device ever. I want to write code to solve problems, and for a large set of problems Javascript inside a web browser is fairly useless. Javascript is great if your economic model is getting as many users as possible and then getting aquhired before you run out of capital. This is the case for a lot of people on HN, even if they don't realise it. However I'm a small time developer, not in SV, who programs because I enjoy solving problems and helping people, not to get rich. I'm only really interested in whether $(number of people who can run the code) * $(how much they can pay) > $(my cost of living) so that I can afford to eat. It means I don't care so long as the platform/language I choose has enough users to pay my bills, it doesn't have to be 100% of people. I realise that the industry giants at Google or Mozilla don't really care about people like me ('life style business' is usually a term of derision on HN). In a world of web based operating systems that only run web apps I would end up stacking shelves in the supermarket or on the dole because I dislike that technology stack enough that I can't be productive in it. That is why sometimes I bitch about Javascript.