Big Ten schools are larger and generally have incredibly passionate fanbases. Add in that UConn fans had another team in the Final Four in a huge game elsewhere in the country and just probably paid a crapton last year, you can imagine they may not have as many.
But, again, I think people here tend to underestimate fanbases of schools like Purdue because we associate fanbases with winning. That's a very New England thing, I think (it's everywhere, but especially New England).
That said, if UConn wins this weekend, I think our fanbase takes another big step up as I suspect there will be a ton more national bandwagoners hopping aboard. Sort of like the Warriors, or like Duke in the late 80s-early 90s.