How come background checks aren't mandatory?

I just realized the small icons above host name, I just booked and did a meet and greet with a host with no icons. I assumed that Rover did look into host background considering that they are publicly advertising these people online. Doesn't that opening your service up to a potential lawsuit. What if a Host has a cruelty to animals charge against them or domestic violence due to anger problems. Why have background checks at all it they don't mean anything? What does that really say about your safety policy? One could print it out and place on floor for the dogs to eliminate on.

Good service but could be great with a few extra measures: daycare required before boarding, background check, a booklet to give to host in basic dog care.