I'd argue that for Qt this approach makes sense because they provide a well defined API that they stick too. The developer can also ask for specific component if it just want them (like QT GUI, QT SVG...).

I agree that this is more problematic with less common, more buggy libs where the API keep changing, but in this case it's quite easy to check for specific files, specific functions, ...

All this assumptions have huge consequences in terms of velocity and ease of use.