Right. Build and runtime dependencies are a separate matter. But for runtime dependencies, it's easier for developers to supply an OCI image, AppImage, or equivalent, with the exact versions of all dependencies baked in, than to support every possible package manager on every distro, and all possible dependency and environment permutations.
This is also much easier for the user, since they only need to download and run a single self-contained artifact, that was previously (hopefully) tested to be working as intended.
This has its own problems, of course, but it is the equivalent of vendoring build time dependencies.
The last part of my previous comment was specifically about the practice of distros carrying build time libraries. This might've been acceptable for C/C++ that have historically lacked a dependency manager, but modern languages don't have this problem. It's a burden that distro maintainers shouldn't have to worry about.