I've seen this argument a few times, but i'm not sure where it comes from. As soon as you leave your house, you risk crashes and injuries. You could even fall down your stairs. But how is CX any more dangerous? No large peloton, no cars, camerabikes. Unlike road racing, excellent knowledge of the parcours (it's only a few km long, and everybody gets plenty of time to examine every corner and every obstacle before the race starts). Extremely low speed, usually single file, no mass sprints at 70+km/h. Crashes usually mean, falling in the sand, the mud, or grass, at 15km/h. When was the last time we saw an injury in CX like the one of van Aert, Evenepoel, Jakobsen, Froome...? How often have you heard of a CX rider breaking his colarbone? Not a week goes by during the road season, or someone somewhere breaks his colarbone.
I'm sure an average CX rider falls/crashes more often, but more often than not, there are no injuries at all, other than a scuffed knee. Last week van Anrooij cut herself in a disc brake, which i do not consider an injury related to CX, it could happen in any cycling branch, as most use disc brakes now. Last year Toon Aerts broke a rib (i think). Sure, if you want to be the hero and jump the barriers when you can't, you could crash, but even there, there aren't many actual or serious injuries to speak of.
As for Stybar, he quit riding for results in 2013 or 2014. When he enters a race now, it's just a form of training. Surely not just physical, but also to maintain bike handling skills that he can use in cobbled classics etc. And it's probably more fun (and financially interesting) while no more risky, compared to training on the road, in daily traffic.