main reason is honestly just that it really helps out in utilizing the games gimmicks,for instance Embers' and Depths open corners offer a lot of sections where one can make great use of the games air control to break free from the track and do some quite wild cuts (e.g. using the edge of a platform as a ramp by falling off and going back on track, resulting in a jump that can cut a corner, using a jump item to jump to a near road etc.).
The huge amount of air control on offer really just comes out to shine due to this kind of course design, Mistylake as a whole is just a joy due to the amount of offtrack movement you can do, sea of tranquility, the outside world and Depths offer so much free movement unlike what most other games of this genre could offer and its tracks such as these that people are still playing the for game actively online.
And as for drifting, it is extremly important which also leads to the courses being designed the way they are. As you are meant to always be in a drift to not lose out on your boost (unless you of course hitting a boost), making the corners as tight as they are results in some quite nice drift chains and switch boost routes, though i must admit that on first playthrough it is extremly hard to judge what kind of corner is going to follow due to improper visibility, but after learning the layouts the tracks really flow together nicely and offer a multitude of options for paths to take with their own trade offs and risks.

as a community weve made several modded tracks, some that were ripped from other games (e.g. mariokart), but with those ripped tracks it is quite apparent how different skydrift really plays from those other games, that half of its essence just gets lost when there is no free movement and verticality or exciting closed of spaces with risky corners. (i also added a thwomp to a custom designed track i made and it really doesnt work all that well here, i tried)

And yeah, guess its just part Touhou for it to be hard at first sight, but learning the games mechanics and what is to come resulting in a gratifying payoff once everything just clicks together, be that impossibly looking spellcards in Mainline touhou games, or orthodox course designs here.

Yea they are a bit frustrating when first encountered but after you master them the same tracks are 100% the most satisfying, if they were all Mari-Circuit no way could not maintain any long term interest personally.
Controller is a must for this game btw.