As it stands now, BCV guests have zero reason to hop.
I can think of a couple reasons:
1) Pool hopping to MK pools on days when they do the MK park. Members here have said that they do this - pack swimsuits in the morning, head over to the Poly or WL at 1:00, swim for a few hours and head back.
2) I think there aren't many, but members who prefer other pools. Someone here has kids who prefer the BW slide to SAB and so hop over to BW. I'm not a SAB fan (I think its really hard to watch your kids there - and that lazy river is very deep) and I think that some parents may choose to hop when their kids are at the "independent but watch them" age in the pool - but they still want a slide (so the don't do the BCV quiet pool). Now young kids and the sandbar - all over that. Young kids and the kiddie slide....great. Older kids who don't need an eye on them - lots of fun.
I doubt many DVC members hop. And I agree that probably fewer BCV guests hop than other members. But I'm pretty sure a few do.
Also, I think 100 people average a day to SAB is believeable. There are 1000 DVC rooms on site now. Say the average room holds four people. That would be 4000 DVC members. If, on a given day, 1% of them hop somewhere, thats 400 people - with SAB being the likely most popular destination. Pool hopping does't have to be very popular to have a big impact on the pools.