There is no clear one-answer-fits-all, but for me it is:
The usage ergonomics of Illustrator's snap functions are better. Yes, they are overzealously configured by default. *
Grid snap works differently, and ties to arrow key nudging.
Illustrator is built on EPS and then from that on PDF, and not SVG. This is a really big deal if you ever intend to publish your stuff on paper.
Basically this allows you to work with spot colors and CMYK. It's tied to Adobe's color management engine.
This also makes Illustrator a much better general vector tool for salvaging stuff from other documents. Though something has to be said about using Inkscape to remove DRM.
Easier handling of multiple objects nodes at the same time.
Illustrator files can be linked to InDesign and After Effects in a way that Inkscape cannot. This is a huge deal for several industries. Illustrator also works seamlessly with Photoshop but that's often less of an issue.
Adobe's font engine.
Note: The functions 1-4 are the only things I ultimately care of.
But yes, Illustrator is needlessly hard to learn. Mostly because Adobe wants to justify their new features and hide the old ones. Forgetting that you cannot actually do anything in Illustrator if you don't learn to use features that have existed since the 1990s.
So to effectively learn Illustrator you need to start by rearranging the GUI, and disabling two features and learning to avoid using the black arrow tool.
But at the end of the day you can't judge an application with a few weeks of usage. I mean I use Inkscape every 6 or 7 days, its passable. But wouldn't rely on it.
* Designing good snapping is hard because there are contradicting requirements. The defaults are OK if you want to use Illustrator as PowerPoint but really...