Because if you're selling a computer, and it has a USB 2 port, you don't want your spec sheet saying "USB 2" while others have "USB 3", but it's hard to upgrade your stuff mid-cycle, so you get "USB 3.1" to be defined as "USB 2" so you can look at least competitive.
Neither is true. Because those are document generation numbers being used as marketting terms by the product manufacturers.
USB-IF should refuse to certify manufactured products that doesn't use the marketing terms that do include the actual speed. But it is funded by those manufacturers so they do whatever they want to confuse and trap consumers.
