For the Proposal of Mythology.
Should the person who started a proposal automatically become a moderator? If I make a proposal I want it to be a website in which I and others feel comfortable.
Other than what John pointed out, there are a lot of other reasons too.
Proposal creators disappear many a time after creating the proposal.
Other users have a greater impact on the proposal than the creator by bringing in new followers, sharing, and spreading the word.
Many users come together, discuss, debate, explore and then clearly define the actual scope of the site. The creator essentially threw out two lines on the internet at large. It is these individuals who turned that line into a scope and possibly viable site.
Proposals rarely go out into beta in the same form in which they were initially suggested.
So, a big
The contributions of a proposal creator are rarely deserving of a moderator position on the beta site. In the cases that they are, then we dont really need this discussion at all.
(Dont forget, the creator gets a significant rep bump of >1k rep for a proposal going to beta, if recognition was a reason that motivated you to suggest this)