I’m open to being wrong, but my domain is not and has not been web apps. It’s mostly been things like satellite antenna control software, quantum computers, scientific computing, and AI. Each of those domains, in my experience, has been firmly grounded in open source. (It does not mean, of course, that the end product is open source.) I recognize there are some domains that are steeped in closed source solutions with closed source developer tooling with no viable alternatives, but IME—as limited as it may be—it’s uncommon.
What programming language stack do you (and a lot of other developers) use that’s closed source with no realistic open source alternative? It’s not C, Python, Java, Ruby, JavaScript, Lisp, Fortran, C++, PHP, Perl, Go, SQL, Rust, Objective-C, or Swift? (All of these, of course, not only have industrial strength FOSS implementations, but the first or second most popular implementation is the FOSS one.)