This is just my opinion based on playing sites since like 2008. I personally think when opening to the public the players go in with a wrong mind set. People join, get bored quick and leave little feedback. I'd see 200ish people join and like maybe 10% are actively doing bug reporting or suggestions. Some people also put a frustrating importance on low account numbers. (Hell I had a person who wanted to buy my aywas account)
Also I'm going to be blunt, I do not believe in paying to get in early. Maybe because I've been burned a few times. Aside from a low number you run the risk of paying for nothing. While I did not pay for it, I do remember winning a alpha for a site that was charging $10 only to find it was a few coded pages and a forum. As for the two sims I did pay for one had hardly anyone playing( like 5 active people which left a lot of features unused) and the other just stopped updating for over a year. Honestly I'd rather have a donate option for a alpha/beta because the account bundles and cash shops really hard for me to justify buying. What am I going to do with 10,000 credits when the cash shop has 5 items or i paid $10 to test a site that is a few pages and a forum with like 8-12 active testers.