Earlier quoted context omitted.
How? Are they more likely to get in accidents? And even so wouldn't that justify higher premiums, not complete exclusion?
If you drive more, you are more likely to get into an accident. This is why taxi drivers have to pay more for insurance than commuters. They definitely should pay a higher premium (or a premium scaled to usage).
Not to mention, in my experience taxi drivers have a tendency to want to get to their destination quickly!