The Aramaic of the Yerushalmi is more difficult because we are used to the Shakla V’tarya of the Bavli, which the Savoraim and early Geonim went over meticulously to establish a Girsa and rules of Shakla V’tarya to ease learning. No such thing happened to the Yerushalmi. Therefore there is a much less uniform Shakla V’tarya and it’s much more difficult to understand.
(The same is true of parts of T’murah, M’ilah, and to a lesser extent Nazir.)