Pre-ordering an item is a vote of confidence in that product. In some cases, supply may be limited and the pre-order allows an earlier acquisition before the product sells out (e.g. Tesla electric cars) but in other cases, the supply is unlimited, as with a digital album.
These latter cases are particularly interesting from a desirability standpoint. Why would consumers pay earlier for something when there is no distinct advantage for doing so? Standard economic theory would hold that this is irrational, but regardless, there is a strong positive benefit for the product itself.
When consumers are lining up to pre-order an album, it gives others the impression that the album is scarce in quality, a recurring theme in design desirability. Further, it turns the consumers who have pre-ordered the product into invested advocates for its success, as they seek to justify their purchase to themselves and let others know that they are ahead of the curve.