hey, i'll shine some light on the matter!
i'll admit the level order of the levels isn't perfect; designing levels was the heaviest task of this jam - about half of the development time went into creating all the different rooms - but the time we had for determining the order of the levels was much shorter (less than an hour).
we definitely wanted the levels to have some fluctuations in the difficulty curve, exactly for the reason you've stated - as a means to keep player engagement high - 'rewarding' the player with some easy levels after a very hard one makes them feel less tense and gives a more powerful sense of progression (which are both important for jam games).
i completely agree about the hard levels though, the spike is too big. the way i'd solve this is to tone down these harder levels, make them a bit easier to solve, with hints like visual cues or a more refined room layout (level 16, which a lot of people get stuck on, would've greatly benefitted from such changes).
all in all i'm happy people are taking notice of this problem, and we'll make sure to give it more thought next time :)