Purdue just didn't license merchandise like the other schools did, and that they never got Purdue gear because they were so tight with the licensing of merchandise.
This is something I complained about before and believe this is a killer to the "brand".
A few years ago, Stadium Pants were pretty big with all the southern schools. These were chinos covered with the school logo. Well one day they had Purdue pants for sale and I ordered them. I got an email a day later telling me that Purdue had rejected their licensing agreement. Well technically they didn't have one but every other school agreed to it so quickly they didn't anticipate Purdue saying no.
TL/DR: Purdue sucks at marketing themselves