It would be that because the degree of transparency between Homura and Mami is greater in this universe, Mami perhaps did not feel the need to tie Homura up like in the series. I think this entire doujin is what would happen if communication between the girls let alone Kyubey was far greater.
...Both of you!
Hurry, make a contract with me!Decide what your wish is! Quickly!!That won't be necessary.Madoka! Sayaka!This guy will be stopped by------the two of us!Huh!?I still have my head, too!!