The academic outsourcing sites actually send out notifications to writers who have had inactive accounts for more than a year to remind them to log-in so that the account will remain active.
It is very possible that they did have that many writers on staff but then the writers probably got embroiled in some payment issues with the company (the most common reason that they would stop checking into the account) and decide to just let the account "expire".
This was probably one of those instances. The company does some "spring cleaning" every so often, specially when the orders on the server become less and less so that there are not enough orders to go around the existing writers accounts. When the "hot" season, meaning the regular school year starts up, they open the vacated slots to a new set of victims, I mean writers. Then the cycle begins anew.
The number of writers that you saw listed are probably the number of currently active writers on the site. Meaning they have ongoing work. That count is different from the overall tally of writers registered with the site.
It can get confusing at times to try and figure out how many writers there actually are so I stopped trying to figure it out a long time ago.