Let's consider Visual Studio Code. It's OSS — still, I read the codebase a couple of times and I wouldn't venture into hacking into it — it's too large.
Being OSS enables hackability, it doesn't provide or guarantee it.
I wasn't claiming that OSS necessarily enables a specific individual to be able to hack on it.
Just in case of your example if as a TS programmer I learn about a new code IDE that is open source and is written in TS, I might be more motivated to go check it out and explore it. So that fact does deserve mentioning - that is all I was saying. Whether or not I eventually end up contributing to it depends on a lot of factors and is besides the point.
Being OSS enables hackability, it doesn't provide or guarantee it.