Bessèges has been running for ages, basically always without major incidents like this and yesterday's, and often on the same roads (today's stage is literally in there every year). Unless the organisers are short on manpower or something this year, I struggle to see how this is because they have ***ed up. Think it's more likely that they had bad luck running into two moronic drivers.
Also, even if the car came from a roundabout, it's not necessarily the organiser's fault. I work for a company that does highway maintenance and every year, there are more people who will deliberately ignore very visible road closures, resulting in dangerous situations. The kind of person who does that is also the kind of person who will brute force their way past the motors guarding the route. Stands to reason that the rise in antisocial behaviour post-Covid is going to result in more incidents like this, even when safety regulations are still being followed to the same extent.