It's a model that has worked for them for quite some time. At least each one has an item that is worth doing it for a certain job. Even the avatars, practically each one drops something decent, where are you getting 4 have 0 good drops? Titan has Shuriken, Garuda has Occ quick cast+2% ring, Ramuh torque still has highest macc w/additional FC. People seem to expect skirmish/delve type of equipment enhancements and those won't be coming for a while. People were begging SE to go back to this model because they hated things getting outdated, and yet now they complain. This model is exactly how the old school stuff worked, you had tons of bcnms that only had one drop someone might have needed. To answer the second part, they might just want people to experience nostalgia fighting old bosses at high difficulties, maybe not even for the drops.

I'm sure they plan to add a ton more hard mode battles due to the amount they can pull from in the game. I doubt they can seriously make every single one drop an item that makes people go "OOOH that is amazing". If anything they should add cinders, heavy plates and linen pouches to some of these with lesser drops.