It's part of the culture up North.
First, we may not produce a ton of 210 lb athletes but we churn out 6-6 320 lb grinders like it's nothing. Go into any small town in northern Wisconsin and there will be a family of giants. People are just big here.
Second, it has become a point of pride to play Oline at Wisconsin for in state kids. Most of the really good ones commit after their soph or jr camps at UW. Outside of Iowa, no B1G schools even put much effort into getting guys out of Wisconsin, they all know where they are going to wind up eventually.
Third, there is only one D-1 school in the state so most HS teams run some form of UW's offense. 7-7 is not a thing here. That means these linemen grow up in a pro style system so it isn't a huge transition when they get to Madison.
We have changed line coaches a half dozen times, gone from a zone scheme to a gap and back again, the only constant has been Alvarez and his emphasis on line play. There aren't many schools where the lineman are the biggest stars. When he took the UW job in 1990 he famously said "Our heart and soul are going to come from Wisconsin, but our hands and feet better come from somewhere else." 30 years later it is still true.
