This game is sorta like HHS--it's kinda from before the era when game development engines were the established things that they are today. Flash, in those days, still seemed like a legitimate choice for developing a platforming game.
So, yeah, expect to see things drag for a while. Like folks have said, the dev only recently decided to switch over to a real game engine. It's always nice not to have to invent the wheel on things like collision with platforms. I mean, game development engines exist for this kind of dev: can draw, can program, motivated enough to actually do both, but doesn't need the burden of starting from square one with absolutely basic stuff.
(Of course, I like this game, so I'm going to be a bit of a cheerleader. Cute pink almost-furry catgirl, lewdness meter, outfits/clothes breaking, monster sex, etc.)