Not saying I disagree, but model aircraft don't require tail numbers or transponders - in fact the FAA "may not promulgate any rule or regulation regarding a model aircraft"[1] that meets certain criteria - so what makes drones special?

Larger drones could go over 55 pounds weight, and that might permit the FAA to require vehicle registration. But that's beyond the scope of my knowledge.

[1] https://www.faa.gov/uas/media/Sec_331_336_UAS.pdf