I will not and cannot contact former committers.
Most of the Mathematica questions on the math.SE site are tolerated and would be immediately closed as off-topic if a Mathematica site existed. Many of the CAS questions on Stack Overflow do not get good answers and are certainly not welcomed. Almost no one wants the Mathematica questions on these sites except the Stack Exchange moderators who are not concerned.
In the past months, I have repeatedly told users on math.SE who posed a Mathematica question that they might want to commit to the Mathematica proposal. This is painful slow work to gather support from people who are actually interested. Now, this work has been destroyed by the Stack Exchange moderators because they have judged that the proposal should be held to much, much higher standards than others based on their original faulty assumption that there is already a big expert community on Stack Overflow who wants to segregate for personal vanity reasons.
The Mathematica commitment was very close to reaching 100 commitments and thus being advertised, rendering manual advice to individual users unnecessary.
It is this disrespect of my time and effort that annoys me the most, and I will certainly not invest more time when there is no guarantee that this proposal is treated with as much respect as others.
The existence of a Mathematica site on Stack Exchange is not very important to me personally, but the respect of my time and effort very much is, because this concerns my investment on all Stack Exchange sites.