The thing is, this debate as been done to death in the past, and we surely all know by now that to a large degree it is all about traditions, and traditionally some sports decide their world champion in one way, some in another, in some of them it's a big deal and in others it hardly matters at all (or doesn't even exist).
In chess we have (or almost always have had) a champion based on a match between the champion and a challenger, and that's the tradition. But there's more to it than that, because because other ways of deciding the title don't necessarily seem to be available to us. An annual circuit with players accumulating points towards a title? We don't have one one which we can sufficiently rely. A two or three-week knock-out tournament at a single venue? Plausible (and great for rapidplay) but it's not what the players or the fans want and was very widely mocked when FIDE operated that system.
Which leaves us with the system we have, a champion in possession of the title, the search for a challenger and a match to decide. It's pretty rickety and flawed, for all kinds of reasons - the champion may die, or refuse to defend their title, or go rogue, or whatever, the system to decide the challenger can never be relied on and the length of the matches is no longer satisfactory. Most of those problems can be attributed to the absence of money in chess, which isn't a problem ever likely to be solved for any length of time, but which also makes alternative solutions like the annual circuit even less satisfactory.
So what can you do, but stagger on? I'd much prefer a longer match, say sixteen games, but as has been observed above, what this means in post-Soviet circumstances is professionals being asked to play an extra week, and organisers booking expensive halls, for the same money as twelve. Do we think that's going to happen?
"Do you play chess?"
"Yes, but I prefer a game with a better chance of cheating."