SPYJ options volume

SPYJ are the 1000 share contracts, why are there volume so low in comparison to standard SPY? The bid ask spread is big, was going to use it as a substitute to trading SPX options

 

Why would you trade these over spx?

If it ain't broke, why fix it?

 

because IB charge > $1.5 a leg commission for SPX, ~ half that for SPY.
any idea why SPYJ are like that?

 

mag...why not just do ES options?