If you have Uninsured Motorist coverage on your policy, that's how you get compensated.
If you don't have Uninsured Motorist coverage, you won't get compensated.
Oh sure, you can sue the owner of the responsible vehicle in court. And you'll win, no problem there. But winning in court and getting paid are two different things, because the court can't force someone to pay money they don't have. And in case you didn't know, people who drive without insurance usually don't have millions of dollars just sitting around. They're usually broke and useless, in fact.