The increase is a likely, largely due to people trying to game the system; Sellers whose accounts have been frozen, those creating extra accounts for when theirs do get frozen, scammers 'cultivating' fake or throw-away accounts to themselves scam with or sell to other scammers/ebaY sellers, and others created strictly for the purpose of fraud.
It's a HUGE industry. Paypal loves it.
Hahaha.
Even so, I bet chances are good that the numbers of inactive and/or closed accounts are growing faster than active accounts.
(I doubt paypal subtracts the numbers of closed accounts from their figures, instead they just become counted as 'inactive', much like ebaY counts all fraud transactions and NPBs etc as successfully completed listings)