If you can’t accept the risks then you don’t ride there/anywhere. You even have to sign a disclaimer (not sure how well that will hold up).
It’s the same as any other place we ride bikes, there’s no guarantee that you will be found if injured, so why do BPW need to take on this additional responsibility other than that you pay a small amount to ride there?
You have to accept responsibility, take precautions and minimise the risks as much as you feel able to. You weren’t riding alone either so you had already minimised that risk.
BPW did the last rider sweep when they opened. I guess the actual practicality proved too difficult and opened a potential can of worms wrt liability.
Clearly this crash has scared you so hope you feel better soon and get back on the bike.