You will often have recipes that are developed specifically to use up items as they get older and have lost some of their qualities as compared to when they're fresh.
Old bread can be turned into Pan Perdu ("Lost Bread", aka "French Toast"), croutons, or bread crumbs. Although any of these dishes can be made from fresh bread, they often work better with older, dryer bread.
It's very likely that this recipe was devised as a way for the bakery to use unsold croissants. Although they could be used in a bread pudding, that wouldn't be something that a bakery could sell as a sort of grab-and-go type thing.
It's quite possible that bakeries now intentionally make more croissants than they expect to sell in a day, if they can get a sufficient premium for the almond croissants to make up for it.
For home cooks to end up with a similar result, they'd also want to use day-old croissants to get the proper texture. If you tried to spread the paste on a fresh croissant, you'd end up squishing it as they're quite soft. Although day-old croissant aren't as firm as toast would be, it'd be easier to spread something on. And as John Feltz mentioned, you'd also have more problems if the croissant soaked up significant moisture from the paste (making the croissant even more squishy).