You will have same issue when driving with a friend of your no. Or are you saying they aren't covered in the UK then? That seems to be easily fixable.
Again sure you can blow it up to be a big problem but it's easily fixable and doesn't in itself take anything away from the original point which started this weird insurance thread.
There's a big difference between your buddy paying you $20 to take him to the airport couple times a year and regularly giving strangers rides where you expect to make a profit.
Even if you picked up a hitchhiker and they gave you $20 for your troubles that hitchhiker is not your customer and you don't regularly drive around looking for hitchhikers to make a profit.
It's actually pretty straightforward. That's why the term "sharing economy" is so disingenuous; nothing but doublespeak.
Again sure you can blow it up to be a big problem but it's easily fixable and doesn't in itself take anything away from the original point which started this weird insurance thread.