Has anyone been able to determine exactly WHY Kasikorn Bank Health Insurance is so much less expensive (with no check-up requirement) than other mainstream policies?

It offers far less coverage than a standard health insurance plan.

I was offered their "Health Insurance" last week if I opened an account ( only need passport mister no work permit) when I read the small print it was accident insurance, 2700 baht per year for 50,000 baht cover, same policy with my broker 1000 baht!

How much is it and what is the coverage?

Yearly 17k/29k for those in 60's (higher fee includes OPD up to 1,500 baht up to 30 times a year. Although listed at 500k per year coverage the payment of each disease or accident tops out at 50k In-Patient so really very little coverage if have any serious operation.

I was offered their "Health Insurance" last week if I opened an account ( only need passport mister no work permit) when I read the small print it was accident insurance, 2700 baht per year for 50,000 baht cover, same policy with my broker 1000 baht!

you were offered accident insurance. not health insurance.

One thing, It used to come attached to a special colored debit card. Which I always carry with my Thai DL. In an unfortunate event of an accident the ambulances will pick you up and take you in without question, without a k-bank card they have been known to hold you hostage on the side of the road until someone stumps up with a debit or credit card number over the phone.