"For fun" as in "for travel" or "for visiting people" which is fun. As in the whole "business or pleasure?" type thing people get asked when flying, I think the majority of folks in economy (and maybe all flight) are travelling for pleasure.

As unpleasurable as flight is, it's typically the best and cheapest option unless not going far or you're lucky enough to have nice rail options. So it's still "more fun" than the alternative which might mean extra days of travel time which may even include you actively having to drive.