Welcome to Fedora, @midnight1. Please take a minute to look at the posts in the #start-here category if you’ve not had a chance to do so yet.
As said by @chrismurphy in this post: Kernel & kernel-devel & kernel-header versions - #2 by chrismurphy
I’m pretty sure kernel-headers is only built/rebuilt when the interface between kernel and userspace changes, which doesn’t happen every dot version.
Said that, how are you installing VirtualBox? By downloading the RPM package from virtualbox web site or from the RPMFusion repository?