Is a spare really necessary? Most likely not hence why it doesn't exist in the cmax.
It doesn't exist in the C-Max because it costs money and takes up space. If you only drive on paved roads, only drive where you have cell service, and are willing to wait however long it takes for a tow truck to get there, a spare is probably not necessary (or, like my parents, you're just not physically able to change a tire).
Those cases actually cover a majority of the people a majority of the time, so Ford thought they could get away without providing a spare. But I've gotten a couple flats out in the boonies where I couldn't call for help, roadside assistance or AAA wouldn't cover it (dirt roads), and it would probably take me a whole day (and mucho $$$) to get a tow truck out there.
I've also had a couple sidewall leaks. One was my own fault where I scraped a curb and one was just a puncture that wasn't on on the tread. Plugs are not recommended for sidewall punctures.
So, I paid the money and gave up the space for a full size wheel and tire. I only take it when I'm on road trips. I just wish Ford had made it an option, including a solid place to mount it, either inside or on a swing-away tire carrier.