Hah! How soon 'till some MBA comes up with a scheme to start licensing movies one word at a time?

Re-licensing music is a two-fold challenge. Sometimes it's much more efficient to use substitute music, instead of negotiating for new rights.

First, licensing arrangements for "all marketing channels" only account for the channels that exist at the time. When a new market channel opens up, such as streaming, music labels will require new licensing terms for that channel. If they don't, they might not get paid. (TV & movie studios are just as ruthless as music labels).

Second, in turn, the labels often have to get new permission from artists for the new channel. Tracking down all artists can be a challenge and require resources that they can't recoup.