Ah okay, I was talking about things like electron applications or desktop/server javascript projects. If you want to use $latest_js_web_framework and package it in a distribution, you're going to be in a world of pain (the same applies for Rust because their package management was based on NPM).
If we're going to talk about linux packages, aren't they often written in languages with amazing optimization skills? If I write some C99 code that uses a gigantic library but I only use like 2% of it, my compiler will cut out the 98% my code doesn't use, so libleftpad sounds like an awful idea. That's one reason why packages on linux distros aren't too big.
But I'm talking about iOS apps where, as others have pointed out, the available optimizations suck[0], and as such, I think that having libleftpad.o included in everyone's iOS apps isn't a big deal (note that iOS doesn't really have a nice way to create libleftpad.so anyway AFAICT because all code for your app is supposed to be sandboxed so no one else can mess with or use it). I agree that it would be really cool to just cut out the 98% of $GIGANTIC_LIBRARY that isn't used at compile time, but since Objective C doesn't seem to have that now, I think small things would be a really nice way to give users more space on their phones without removing features.
[0] https://news.ycombinator.com/item?id=14902174