Because this pool has temporary bad luck , means its the best time to jump in 
Please explain this
Well, Its not exactly Mathematically based... more a feeling...
But It is known that eventually the luck more or less evens out in the long run...
so maybe now it will start to even out - meaning some very good luck
BTC guild had a patch of very bad luck..close to -50% over a period of time.
I moved to them and had a nice amount of extra btc because of swing in the luck to the positive.