Time to change the format. It's understandable you don't want to spend your whole career preparing for these long matches all the time. For the challenger it's 6 months of preparing, but for Carlsen it would've been his 6th time of preparing for this in a few years. They have also become less entertaining. 12 matches is long (edit, 14 now), but no one dares to take any risks. Caruana was just defensive and all games…
These changes increase the stakes, incentivize offensive chess, allow the sitting WC to play all the best players rather than one, reduces the time commitment to a single event for the challengers, and allows the WC to partake in the most prestigious tournament.