For the Angel Bird, I'm not sure if Yamato is willing to take that risk. If you'll remember, the 1/48 Angel Birds 1A was on clearance SEVERAL times within recent years, and even now you can find it for up to 3000 yen less than the MSRP from etailers overseas. That version was not a hot seller at all. It doesn't help that the Angel Birds valk wasn't unique aside from color scheme, was from the TV series which in Japan is arguably less popular than DYRL?, was not piloted by any of the main characters, nor was it seen in combat(because it is a air show demo plane in the series).
Sure the tooling on the TV 1A's might be done in 1/48 scale but those were also hand painted IIRC.
As for the Destroids, tooling is done yes, but no new parts were made for those; they are just repaints.