For screenFetch specifically it is because the author of that program has named it "screenFetch" exactly, with the capital F. Check the GitHub, I was confused too until I noticed it.
It comes down to a question of consistency. It's great that Void is consistent about not modifying package names... but howmuch consistency is therefore sacrificed for packages which use strange, inconsistent names?
Some namings make a great deal of sense, for example the
libX naming scheme for X packages. However names like
AlsaMixer.app (the latter in particular blew my mind) should probably be normalized in the Void repository imho. Seems like that is something a maintainer would be expected to do, ensure sanity of packages' naming schemes. Developers and package maintainers can and should think differently!