I never understood the reason for separate Type B connectors when the standard A, micro or now C-type connectors would work just as well and allow people to use the millions of cables of those they already have.
Pre-USB-C: USB A is host, USB B is device - be it normal-size-B or micro-size-B. Those should be the most common cables. (I'm not sure I'd have any standard-A-to-A?)
