Mostly because they both did very well in the OCC schedule. The B10 is brutal this year. There isn't a walk through game in the conference.
Meh. Nebraska has a good OOC Schedule, but I'm not sure they defeated any at-large teams. They have 4 decent wins over what appear to all be NIT Teams: Clemson (#56), Creighton (#62), Seton Hall (#63), Oklahoma State (#70)... 3-7 in league play with their best win being against Indiana (#48), who is 3-7 as well.
Indiana's best conference win was against Northwestern (#57). They do have two very good OOC wins against Marquette (#19) and Louisville (#12). I'm using the Net Rankings, btw... I'll acknowledge that the Big Ten is very deep. But you have to go at least 9-11 in league play to have a chance. Winning 40% does not merit an at-large bid. Would much rather see Wofford or San Francisco get an at-large over an 8-12 or 9-11 team.