you misunderstand what they protect against. If it were simply a matter of covering the exact costs, and they didn't have factors like... oh, I don't know, having vast amounts of cash on hand to be able to pay for your accident and medical bills, or paying their staff, or rent, or administrative costs, then sure, they could just keep track of what you've paid and pay that much back out again.
Oh wait, that's what a BANK is for.
What an insurance company covers is being able to pay the amount you need when you need it. It's not a pre-pay installment plan. In addition, they're providing coverage that is required by law so you can drive your car. You pay X from your example so you're covered. No, I don't think it's unfair that laws require you to have insurance. I have much less trust in the ability of the average person to have enough savings to cover an accident where they're at fault than I do their ability to pay some money each month to a company to guarantee the money will come from somewhere. Again, the X is just to make sure the money will come from somewhere, and much of it goes to paying their employees and admin costs. And then profit. Yes, profit. How dare that private company try to make money! Curse those inhuman monsters! The X+Z is because it now costs more to cover you. Ie, they spend more to cover you, thus they need to make more to make it worth their effort.
No, they're not altruistic, but they went into the business to make money, not to be a non-profit charity. I fail to see how that makes them draconian obscenities.