Electrical – USB OTG Cable Shielding

The more I think about it, the more I'm convinced the reason is not technical. It likely is just to avoid the burden of certifying a device with dual-role OTG capability.

Apparently (see here), testing a device for OTG compliance costs almost twice as much as testing a simple high-speed device. There is also much more work in the design phase, and much more risk of failing the compliance, having to make design iterations, and going through testing again. Since the OTG capability isn't used by many consumers, manufacturers don't feel the need to advertise full OTG compliance.

Instead, they simply certify the phone/tablet/whatever/... for "USB device-only" usage, then use clever marketing wording (claiming "OTG-compatibility", for example), and call it a day.

Because they don't test for dual-role OTG compliance, they are not allowed to use micro-AB connector (or they would fail the simple device-only compliance). So they simply put a micro-B receptacle, and expect cable manufacturers to provide adapters such as the one shown above (although such adapters are officially forbidden by the USB spec - but cable manufacturers don't really care).

Also note that the logo on the cable above is not the USB logo that is subject to strict licensing. It is the "trident" logo, whose usage is much more relaxed. This logo, for example, does not imply that the item has passed the USB compliance tests.

This is because Mini USB has been essentially phased out as depreciated, the newer standard is the USB micro-B bus, which is compatible with 3 times as many sockets as a mini USB.

The mini USB never caught on, not only because of plug, but because of its size. If one were to use a mini USB, the height was very similar to the USB A plug, so those were used instead.

Male SM components were exceptionally uncommon, as there are few uses for devices which have such small hard points. The smaller ports would often break and bend easily compared to the large ports. On top of that, smaller USB form factors were designed specifically for a device that would need a small socket due to space constraints (EG: phone, console controller). If someone needed a Device that plugs into another, there wasn't really any reason that A couldn't be used.

However, There are still many mini A-type USB male SM components out there, I have a sneaking suspicion you're looking on common shopping websites, as opposed to component distributors, the largest known to sell to consumers are Mouser and Digikey.