Import and export are different. HTS vs. Schedule B. Yes, they’re both based on the international HS standard, but they’re US systems.
Since these are systems that attempt to classify every single item that gets sold internationally, they try to balance how specific they get. Hence almost every heading having some form of ‘other’ category. Drysuits (to stay on topic) are an interesting case to consider. Different manufacturers have used different forms of coated canvas, neoprene, bilaminate, trilaminate, and probably other materials over the years. Each of these could be classified differently, but that would be time consuming and complicated. As a worn item, drysuits are classified as apparel, but they’re obviously different than clothing. Look at the duty rates for undersuits for a good example of why we don’t want drysuits classed as clothing. Drysuits also don’t fit cleanly into sporting goods, either, since they might be used commercially or by municipalities.
On top of all that, there’s also the consideration of precedent in how similar items have previously been classified. CBP has a searchable database of customs rulings, although it’s incomplete.
There is a reason this is a job for lots of people and hasn’t been automated; it requires knowledge, experience, and staying on top of changes.
Again, AI hallucinations are a known limitation, especially when asking for situationally specific information. It’s not how they’re designed to work. From ARL-TR-2224, “Butyl rubbers are copolymers of isobutylene with a small amount of isoprene added to allow for vulcanization.”