Originally Posted by
cyclic
The biggest reason that rad alt isn't used is that most crew change aircraft only have one so a failure would not be good.
A servicable RadAlt is obligatory for night approaches (as you're well aware). RadAlt U/S = Go Around and/or RTB.
Other modern aircraft types are more than happy to make night approaches coupled to the RadAlt which is, arguably, safer than a slightly antiquated baralt/RadAlt matching technique, using ALTA.