They don't? What about 705.12(B)(5). Fastening. Listed plug-in-type circuit breakers backfed from electric power sources that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by
408.36(D) for such applications.
Maybe it is how you interpret the words... is the "that are listed and identified as interactive" modifying plug-in circuit breakers or electric power sources? Without any commas, you may be right that feeding a breaker from a listed and identified interactive power source is all you need to eliminate the hold down. I was reading it the other way (e.g. there could be plug-in circuit breaker that are listed as "interactive" types and only those don't need the hold down).
The intent of requiring a fastener for backfed plug-on breakers, is for power sources that remain energized after the breaker is set to the off-position, or unplugged from the busbars. Examples of where this would apply are generators, utility services, and feeders from an upstream panel to the subpanel in question. Essentially using a branch breaker as the main breaker of the panel. The idea is to make an extra step in unplugging the breaker from the busbar, due to its wires still being energized.
Inverters are an exception, because by contrast, they will automatically de-energize the AC-side, if the voltage is no longer within the tolerance. Remove the voltage, and it ceases to be able to apply current to the line. Inverters first look for a voltage within tolerance, and then after a UL-required 5 minute delay, will begin backfeeding current to the line. Unlike other sources that generate their own voltage first, and allow current to follow when the load is connected.