"With albums being unbundled, tracks are available now for individual download, so the number of units available for sale has increased."
With albums you often get two tracks, and a bunch of steaming crap to fill up space.
With unbundling you can just buy the two tracks, cutting the record companies revenue. They can no longer make you buy crap to get what you want.
Kiss had quite a few pop hits, someone who wants "Beth" is not going to want the Rock that fills the rest of the album (even the few that are not crap).
If you only buy the tracks you like there is no need to buy a "greatest hits" album as you already have your own version (I think Kiss had about 12 different versions). More lost (can't sell you the same crap again) revenue.
The boom from everyone rebuying the same stuff on CD is over. SACD and Audio DVD did not give them another boom of people buying the same stuff again (since they tanked).
But it's much easier to blame the "free-tards" who never buy anything anyway, and would not buy Kiss greatest hits volume 13 even if you took away their internet.