Why should it? There's no payoff, the proposal is gone, the real investment in time and effort composing questions and trying attract support evaporated. Reputation is a pretty poor consolation prize at best, and an incentive to participate in proposals you don't actually care about at worst.
You and Kop seem to be working from the perspective of reputation-as-currency (or wages): something you earn from the work you put in, to store up for later use... That'd be an interesting system (on A51 at least), but that's not how it works - you don't spend it on anything. There's no rep cost to start a proposal, or post a question, or commit, or anything else...
Reputation on Area51, like reputation on the rest of the SE sites, is simply an indicator of participation. Ask a question, given an answer, propose a site and if others find it useful then this is counted. It's an easy to comprehend proxy for something far more complex. So when that participation no longer exists in a meaningful way, then continuing to credit you for it is... Not terribly honest.
Consider this (admittedly extreme) scenario:
- You propose a "peanut butter" site, along with several example questions on the delicious spread.
- Four other peanut butter fans follow your site and vote on your questions.
- Since there are only five people who care enough to participate, the proposal stagnates, and is eventually deleted.
- You propose it again, the same four people sign on, with the same eventual outcome.
- This goes on for some time...
Eventually, you've accumulated a significant amount of reputation... From doggedly pursuing an idea that will never, ever blossom into a real, useful, SE site. If you managed to scour the 'Net for other PB enthusiasts and push it through to the finish, that'd be one thing... But insanity must be its own reward.
Now consider a more likely scenario:
- You hang around Area51 every day, jumping on every new proposal and posting a few questions on each.
- They're decent enough questions, so you get a few votes each time.
- The proposals suck. There's just no great interest in most of them. So over time, they all die.
- You accumulate a ton of reputation, but no one actually benefits from your work.
In the latter scenario, you're putting in a lot of time and effort, you're playing a good game... but it's poorly-directed. The purpose of A51 is to identify sites with enough interest to actually graduate and become self-sustaining, and though you may have the best of intentions, you're not helping.
When a proposal makes it through all the stages and goes live with a healthy level of participation from many users, everyone wins - the users, the readers, the company running all this... When it chokes and dies on the vine, no one wins.
And, ultimately, reputation reflects this.