Excellent point. However, I would add, don't let your dedication to make good hits and your time spent in skill development blind you to the facts that multiple COM hits can fail to stop and that even very good shooters often miss in gunfights. I'm not saying one should plan for failure, that's not wise. But it's also unwise to make a plan that requires perfect performance in order to achieve success.
Why don't you answer the question yourself as an exercise. I'll bet that if you do so thoughtfully you will be able to think of at least three good reasons why people don't carry more than one spare tire and will also, in the process, come up with at least that many reasons why having a second spare tire in a typical passenger vehicle is very different from carrying a high capacity pistol vs. a single-stack or compact revolver.
For what it's worth, I did carry two spares for at least one period of several months, not because I was especially worried about flats during that timeframe but because through a strange set of circumstances I ended up with a spare wheel with a tire on it. That was before cellphones and at the time I was only rarely using my trunk for anything and was also doing a lot of driving through fairly remote areas. So I threw the wheel/tire in the trunk and left it there until I had to take it out to make space for cargo.
