It's not that their API is convoluted, but generally what is being generated by a developer is. It's easy to fall down the jQuery rabbit hole, and start making messy decisions, by just using every possible thing available. Reminds me a lot of early PHP developers, writing spaghetti code because it's easy to do so. I'm currently in the process of converting some of my OWN 10+ year old PHP to Node, and it's difficult to sift through it all. My experience with reading a lot of jQuery stuff is similar. Easy to pick up, and do a lot of magic, which means easy to make a mess.
I disagree that jquery's API is convoluted.
And what is wrong with sugar syntax? One can argue that most of es7 is sugar syntax, but we are happy to use it since it makes your code more terse while remaining readable