Either they created the situation in the first place by riding in a way inconsistent with the rest of the traffic flow (accelerating too hard, riding too fast, weaving in an out of the traffic) or they were not careful enough to handle the mistakes other drivers make.
These accidents are a small percentage (of licenced riders) and yes, they were in the wrong for not riding within their limits/conditions etc. A can only talk locally, but the biggest cause of accidents (bitumen roads) is gravel. Normally, it's left hand corners/twists where cars/trucks slowly deposit it on the road. It's like hitting ice and takes years of experience to recover from a gravel slip. These accidents are very nasty.
Up to a few years ago we had a lot of return riders having accidents. Guys 40, 50 odd with a full licence. In their younger days, they were riding 30 BHP or less bikes. They have a two decade break and then throw their leg over a 160+ BHP machine with no rider training. An accident waiting to happen.
'Unriders'. People with no licence, no rego, no safety ethos, no rider training. These guys are an accident waiting to happen. There are quite a few accidents around my area by these guys.
I'll admit, I'm not angel on the road. After 22 years of riding licenced, I'm still here :). Rider training has made that possible, not chance.
J