Why UASP isn't being used

From looking at uas-detect.h I can see that the ASM1053 chip in your enclosure is indeed supported by the UAS driver (even if it has bugs with large transfers).

You might try modifying your modules.alias file to add support for your device ID. Unfortunately, if depmod is run again by anything on your system you'll have to redo those changes to the modules.alias file.

A second option might be to patch the UAS kernel module to advertise support for your device ID and rebuilding the module. If you did this and push a good patch back upstream, you might even get everyone with your HD enclosure Linux UAS support.