Thanks for the response. One of the most interesting parts of Sketchfab for me is the museum collections (generally 3D scans of the physical artefacts they own). These seem to be often CC0 (for eg University of Dundee Museum Collections (@uod_museums) - Sketchfab or Cleveland Museum of Art (@clevelandart) - Sketchfab). This license makes a lot of sense for a museum and allows the models they offer to be freely used.
CC BY is generally not usable in practice - if I make an image with a number of 3D models (say for an album cover…) there’s no way to actually credit the source of those models and they are often such a minor part of the image that it wouldn’t make sense to do so anyway. In most cases I think people will simply ignore the attribution requirement, but it is nice when a model is officially CC0.