That's suboptimal for many reasons. Package names are not consistent. Installing multiple versions is usually impossible. Huge pain for library authors. Doesn't integrate with build systems usually (even basic pkg-config support is iffy). The command is OS-specific. You can't usually choose the linking method. Difficult to bundle dependencies. Usually out of date. Etc. etc.

it works quite well in practice, and unlike pip things don't break every 2 weeks.