I'd love to see more discussion on this issue, or, at least, an answer as to why they can't have some kind of audio commentaries. Heck, even each actor doing an audio commentary for ONE episode out of the entire series would be something.
Each time a new set of DVDs/Blu-Rays are to be offered, various production teams pitch a concept and budget to CBS. If they win the gig, they must keep to that budget
. There is always a blowout that means some plans have to be curtailed. Commentaries would be the first thing trimmed. IIRC, if they go over budget, it eats into the producers'
profits, not CBS's.
With the advent of podcasts, episode audio commentaries could be created at any time.
They don't have to be on
the Blu-Rays sets; you play them on your computer while the disc plays on your Blu-Rays system. All some production company has to do is pitch the concept and delivery system, sign a licensing agreement, set a price (for iTunes?) and ensure that they can afford to pay the participants' prices for their contribution.
Adding new commentaries is a way of refreshing previously-released boxed sets (eg, the Klingon, Q, Borg, Time Travel and Captains sets of DVDs), some of which had new commentaries and documentaries. In a few years time, when all the TNG sets have been released as Blu-Rays, perhaps commentaries will get added, as a tempter to get people to buy (or rent) them all again
. If Blu-Rays still exist; downloads from a cloud are more likely to be the next wave.