Because manufacturers of actual products are in the USB forum and actively lobby for this shitty naming convention, so their sales of USB4 products don't drop.

Same reason, same companies, same lobbying, which gave us USB 3.0, USB 3.1 Gen 1, USB 3.1 Gen 2, USB 3.2 Gen 1, USB 3.2 Gen 2, USB 3.2 Gen 1×2, USB 3.2 Gen 2×2 (yes they all exist).