Insurance companies (at least auto/property) are regulated by their respective states. They are considered financial institutions, sort of like banks and yet not like them at all.
There are basically 3 ways they can change their rates, depending on the state board of insurance where they do business.
1)Change your rates, whenever you want, we don't care, just file them with us so we know what they are.
2)File your rates with us, and if we don't smack you down within X days, feel free to implement them.
3)File your requested changes with us, and we will let you know whether they are acceptable or not. You must continue to charge existing rates until you hear back from us.
Most states are either #2 or #3. They are already under the thumb of the state to a degree and operating as the state has explicitly given them permission to operate, so no need for bribery.
Now, I suppose it could still happen for law changes, but again, the "government" has to approve everything they do anyway.