If you have a look at how player numbers have declined for any other mmo, their numbers are amazing. Can't forget that WoW come out in 2004, the life span of most games is measured in months.

The game doesn't hold people's interest indefinitely, even of it is a lot longer than most games and probably most people who would want to try the game already have. Also competition is way higher than it was in 2004.

I imagine the implied turn of phrase was actually "struggled to make the numbers". As TheCapn pointed out, an unaccounted for 20% drop in plans is bound to shake things up a little.

If you're slowly-but-surely losing subscribers, going through downsizing, laying off developers, from a business perspecitive it's "struggling".