I can think of two rational reasons for wanting 220 (and probably many irrational ones.*) I'm curious if there are others I missed:
1. Want to use a camera that only shoots 220. I doubt there are many of these, but for some MF system cameras, like the Bronica ETR, a 120 back might cost $150, whereas a 220 back might cost $25. I think similar for Pentax 645 film inserts. Are there any cameras that only shoot 220?
2. More shots per roll. I can certainly see the value of this in a professional context. It also could make sense for travel photography--less roll swapping, less boxes to carry. Is 220 as light safe as 120? I've occasionally had light leak onto the edges if the 120 roll wasn't as tight as it could be or I changed the roll outside. I would think that 220 is less safe to change rolls in sunlight, am I wrong? In general photography, I hate 135 because almost everything is 36 exposures unless I spool them my self, and 36 exposures take me forever to finish, but I know I'm an outlier in that respect. As has been mentioned 220 would probably not be a cost benefit.
For those who would like to have 220 rolls, what are the reasons you would like to see it? Is it one of the things I mentioned above? Or is it emotional/nostalgia? Or would you would just like to try it because its there? I'm genuinely curious.
* When I say irrational, I don't mean bad, just something that is more based on emotion, nostalgia, etc.