Read #7 under "all questions".
Only slightly more than half of motorcycle crash victims have private health insurance coverage. For patients without private insurance, a majority of medical costs are paid by the government.
The last word in the quote should be "Taxpayers".
Except that this isn't true. They've been quoting this "statistic" for years. Motorcyclists are insured at the same rate (or slightly higher in many cases) than automobile drivers. Where this dubious statistic comes from is in the flawed reporting of insurance claims for accident victims. For example, if you are in an accident and you have a cap of $100,000 on your insurance, your company picks up the first $100,000. If your bill is $100,001 the box on the reporting form is checked as insurance didn't cover and this is what the breakdown shows.
As an aside, I don't know where this idea comes from that the "government or taxpayer" pays the rest. Actually the hospital absorbs the rest. They try to get it back from you, but failing that they overcharge all other patients a little bit to make up the cost, which means you pay more for your medical. But since motorcyclists are not uninsured at a higher rate this doesn't really apply to any greater extent than the general populace.
PS The IIHS is a non-profit institute that has been funding questionable studies to "prove" that there should be mandatory motorcycle laws throughout the country for years. They are not exactly unbiased on this issue and many of their studies have been demonstrably flawed.