On 2: maybe CEV IS EY's own personal volition :)
More seriously, probably game theoretic reasons. Why would anyone want to work with/fund EY if it was his own volition that was being implemented?
*Disclaimer: I didn't read any other comments, so this might just echo what someone else said
Well, surely it would depend on the alternatives.
If I believed that EY can build a superhuman AGI in my lifetime that optimizes for the reflectively stable ways EY prefers the world to be, and otherwise believe what I currently do about the world (which includes not believing that better alternatives are likely in my lifetime), I would enthusiastically support (e.g., fund) that effort.
Say what I will about EY's preferences, I see no reason to expect them to leave me worse off than the current state of affairs.
Taken from some old comments of mine that never did get a satisfactory answer.
1) One of the justifications for CEV was that extrapolating from an American in the 21st century and from Archimedes of Syracuse should give similar results. This seems to assume that change in human values over time is mostly "progress" rather than drift. Do we have any evidence for that, except saying that our modern values are "good" according to themselves, so whatever historical process led to them must have been "progress"?
2) How can anyone sincerely want to build an AI that fulfills anything except their own current, personal volition? If Eliezer wants the the AI to look at humanity and infer its best wishes for the future, why can't he task it with looking at himself and inferring his best idea to fulfill humanity's wishes? Why must this particular thing be spelled out in a document like CEV and not left to the mysterious magic of "intelligence", and what other such things are there?