Good question.
I live in Norway and the rules that the Norwegian FAA/Lovdata has issued clearly states that the Drone pilot is the one to blame *in any mishap*, no matter what the cause would be for such a mishap.
So, yes i think that a liability insurance would be good to have.
When I bought my MPP drone (from ELFUN through Komplett.no) I was not presented with the possibility to buy this "DJI Care" possibility either.
So, I think you are stuck with your insurance company and to see if they are willing to sell you an insurance.
It may possibly be a good thing to have the Drone pilot certificate (RO1/RO2 or RO3) when you do try to get such an insurance. Maybe you'll get a rebate
But on that note, it looks like, according to Luftfartstilsynet, that you are really not allowed to fly anywhere where you can *remotely* accidentally harm any people
I have had my MPP drone for three weeks and I'm a real beginner in this field of flying. But it sure is fun