Having a paper accepted for a CVPR talk is a big deal, but the talks themselves are fast paced, given in massive conference halls, and entirely focused on the details of a somewhat arbitrary paper topic.
Also due to visa issue, many talks aren’t even given by the paper’s primary author.
In contrast workshops (of which there are dozens) tend to encompass a clear topic of interest and feature talented senior researchers giving a polished overview of their entire groups results.
On top of that, in a good workshop, you’ll get a real sense of how top researcher’s see the fields/topics being discussed. Also if you want, you can easily ask questions or engage with the workshop organizers.
In short, the workshops provide you with realtime information that is much harder to sniff out at the real conference.