These things are not simple though.
1. Duke hasn't played a non-conference road game in years outside of like 2 in the Big Ten/ACC Challenge. It's like over 5+ years since they have. Why? Because teams like this don't have to. Why would a Duke, UNC, Kansas, etc. go play on the road when they don't have to? Do we want to just go play road games to these teams?
2. For neutral site games, it's a bit easier, but still tough. Remember how the Wooden Tradition fizzled out cause they stopped being able to schedule good teams.
3. You have to be on their level already. Michigan State can schedule a home and home with Kansas because guess what, if either of those teams lose, it's not a big deal. A loss to Kansas is going to be an assured "ok" thing because Kansas has the name. You don't see a lot of the "elite" schools scheduling good, but not elite schools for a reason.
4. Most good teams play in some sort of tournament, which many count on for their "big games". The best teams are in the best tournaments, which means their schedule is in pretty good shape.
5. The Big Ten has taken good steps in increasing scheduling. I don't know if its been done on purpose or not, but the top ACC/Big Ten games used to be played in neutral settings. Recently they've been all on-campus from what I can remember. The Big Ten adding the Big East to a similar series is a same thing. Not every Big Ten program will participate in that every year since the BE is smaller, but they have some quality teams there.
6. This is NOT a Purdue problem. If you think Purdue has all these great teams calling them up to play, you're nuts. It's incredibly hard to schedule, you see it all over the country, not just Purdue.
7. A lot of it has to do with money. First off, Purdue is a tough place to play. It takes convincing for a coach to want to come into Mackey. Secondly, a lot of schools ask for money. If we aren't dealing with much of a budget for that, then we don't have much to offer teams. The mid-major conference teams are looking for cash.