At KSU calc 1, 2, 3, and DiffEq are all 4 hours each (totaling 16). It is common at most universities that these 4 classes total 16 hours. Some schools do it in 5-5-3-3 to get to 16. KU is a little different once you get past calc 2, but both calc 1 & 2 are 5 hours. That is why they would probably require 1 & 2 to transfer in as just 1. It's not that it's "harder", they just organize the the classes different. They cover more in 1 & 2 than KSU, but cover less in the next 2 semesters in finishing the calc string. At the end of 4 semesters you've covered the exact same content with the same difficulty.
Fort Hays uses the 5-5-3-3 system has has the same transfer issues. One system isn't harder/easier, it just makes it difficult to try to match classes up when they use different systems to get the same end result.