Depends on how you want to work it out. Insurance is a fixed cost. As you rightly say, it's a cost which you have to pay, whether you drive 1 mile or a 100,000 miles. (you could say it could be a variable cost, as you may have to tell your insurance company your annual mileage, but usually, it's unlimited). Same with MOTs, and PH driver's, and PH vehicle licences.
Also consider whether you use your car personally, or you just use it solely for Uber, and have a personal vehicle for your own use.