Gaga is very dance and Synthpop which those Europeans can't get enough of...Katy is very sweet and all-American in a sense so it doesn't really make sense for some techno-hungry Germans to use her as much
Gaga is still more global
one single didn't achieve what katy's did doesn't make gaga less global
let's not forget about the tour receipts & album sales which is more important than the singles sales