Even though Vortex's popularity has been declining gradually over the years, it still give more rides than people think (it's a people eater - so yes there will be many times when it's a straight walk-on, but lines don't necessarily indicate ridership!)
As of 2014, it still got over 1m riders.
Granted, it's probably well below that by now, but I could imagine its still in the 750k range.
As far as I know, Arrow loopers are among the most inexpensive coasters to operate (as is most sit-down coasters with a traditional chain lift.)
Whatever Vortex's ridership is now, I still don't think the yearly total operating cost / # of riders is high enough to justify its removal.