Shimano have a habit of making specific stuff for their high end kit and then discontinuing it – it’s happened with road octalink stuff on Dura-Ace I think.
Not really, quite the opposite in fact. Here is a Dura Ace Octalink BB, a part that became obsolete 9 years ago still with reasonable availability. Likewise here is the XTR one, now obsolete for 10 years.
However… they are damned expensive, more than when they were current in fact, and far more than HT2.
The M951s were great cranks, but the M760s are lighter, stiffer and cheaper to maintain. Ie save for the ‘bling’ and the exclusivity factor they are to all intents and purposes better than M951s.