Because they are large codebases with their own technical debt. You're not doing a full rewrite, but just make what you need for you own codebase.
Ah, I think I see now. Essentially the dependency module is unnecessarily large and (for your own use case) ships with extraneous features/“bloat”.
If the parts you need from a larger third party library are small and simple, that makes sense. But I don't think the general idea of reusing battle tested code across many projects is obsolete because of AI.