It's true that many of the users aren't active on the site despite having an account.
Even I had previously forgot my email and password to freebitco.in account and had to create a new account.
I guess there will be many people with similar case and so the real active number of users will be far lesser than the number of accounts on the site.
I tried to find where I saw the story that some inactive accounts won the weekly lottery... it turns out that some "forgotten accounts" have active referrals that earn them sats, RPs, and of course lottery tickets. At least I remember that, but I can't remember when and where I read it.
The total number of registered users on the site doesn't impact your opportunity to win the top prize from free rolls.
Just like it's not so important how many lottery tickets we have. Often clicking on the free roll button and having more tickets can slightly increase the chances of winning, but only slightly. So there are certainly those who will never win top prizes, just as there are people who will be lucky and take more top prizes in some period of time. It's life/gambling...
