Arbusers

Hello, I see that the amount of exchange in term of cash in the betting exchange is less than before. In PIWI it has decreased a lot for one month.
I see also really "low alues" on OrbitX, PIWI, Betfair ?

Which bookies propose the more of money in term of exchange ?

I see also that the values are not the same between the different bookies. It could varie from 50% or much more . How it can be explained?

Thanks.