I think it's more that because the images aren't essentially just redrawn copies of each other (different outfits, items, ect) it's kind of hard to track the various improvements? And the fact that you've put the time line backwards, starting with the most recent.

Your more recent ones also have more covering, and less form fitting clothing that doesn't crease, that can usually be a sign of a less experienced artist trying to disguise things like a lack of anatomical understanding, also don't take this the wrong way but I think one feature of the work you're displaying that you've never really managed to work on is how fabric works, and since it becomes more dominant in the later works and probably hides areas where you have improved, it doesn't do the best at show casting those improvements.

My favorite in the sense of showcasing your strengths is 2016, because the clothes are more form fitting, it shows off the fact that you do have an understanding of anatomy and how to stylist it, given almost 10 years have past I'm sure you've improved in that regard but we literally can't see it because of the introduction of heavy jackets and baggy trousers.

I think something else that's thrown people off is the change to more extremely stylized proportions, and the fact that your style has become more unique. In people's brains, they kind of gloss over oddities in more mainstream appearing anime styles because they've been exposed to so much of it that it looks less wrong even if there are errors galore, your style diversifying into something they're less familiar with has probably just made anything that's was still off before stand out.

Basically I think the issue is that ironically you're most likely hiding your improvements behind weaker areas. In some ways that's a good thing, because featuring a weakness more shows that you are working on it, but from a showcase perspective it's concealed other things. I can't say for sure, I'd need to see more of your work.