At its core, Illustrator (or any vector drawing application) draws lines, geometric shapes and fills those shapes with color. That’s basically it — beyond that it’s just permutations of those core abilities. The code underlying a vector drawing is built around geometry and algebra. It’s not at all a painterly or organic approach to drawing.
It’s great for typography, logos, page layouts and similar purposes that are basically, just hard-edged shapes filled with color.
Your work is looser. Illustrator is tight and precise. Your work looks hand-drawn. Illustrator excels at creating geometric objects.
So trying to create something in a hand-drawn style in Illustrator is a bit of a battle against what Illustrator is best at. It’s doable to an extent, but the more one pushes Illustrator in that direction, the more difficult it becomes to cut across the grain or pedal into the wind.
Illustrator can easily draw a perfectly straight line, a perfect circle and fill that circle with a precise color, which are things not easily doable with hand-drawn artwork. Conversely, it’s difficult to use Illustrator to simulate a hand-drawn look.
Just for the sake of an analogy, a cello produces a rich, emotional, complex sound, whereas a computer can easily produce a perfectly clear tone at a single precise frequency. A cello can’t do that, but today’s computers have a great deal of difficulty simulating the complex timbre of a cello.
I’ve seen lots of illustrators struggle with learning vector programs. Their brains are wired to draw things by hand and they get frustrated that a vector-based computer drawing application just won’t do what they want it to do. Assuming they don’t give up and they work at it long enough, one of two things tend to happen: (1) they get pretty good at difficult workarounds and using the programs to do things that don’t look at all like something done in Illustrator or (2) their style begins to morph into something that plays into Illustrator’s strengths rather than its weaknesses.