I think that just kind of boils down to the whole big name thing. For example, David Gilmour just did his On An Island tour and played a bunch of small, intimate venues. However, if he tours with Pink Floyd, he fills huge arenas. Paul Stanley just did a solo tour and played to a couple thousand people a night, but when he tours with Kiss, they bring in like 5 times that many people. When a singer from a big-name band (or in Chris' case, two big-name bands) does a solo tour, most of the time, unless they're on a bill with another big act, they won't bring in a whole lot of people.