I've definitely been thinking the same thing, especially since most of my vehicles run very large tires on relatively small platforms.
I ditched carrying a spare wheel many years ago, and have been taking the tire less and less. Not having the tire mounted on a wheel allows me to carry ( a lot of ) gear inside the spare tire. I also have a round cooler that fits in the middle of the tire.
Pushing the idea further, a spare tire only fixes one issue. Having a good tire repair kit can fix many issues ( as long as you catch them soon enough ). A good plug, patch, and tube setup still takes up FAR less space ( and weight ) than a full size spare tire. It does have some additional risk, but so does off-road travel in general. There are many aftermarket TPMS systems that can be retrofitted to older vehicles to allow keeping a closer eye on tires.
Having the ability to break down a tire/wheel will be a next level skill for many people, but it isn't THAT difficult to learn. It is one of those skills that will help you fix many issues, not just a single tire issue with a spare.
You also need to have a good onboard air compressor system.....again....that helps fix more than one issue.
As mentioned, motorcycle guys do this kind of stuff all the time.
Some people are going to be(come) more comfortable with it....some people are going to try and find space for 3 spare tires....