Do any other ISAs have compressed encodings in wide use? It seems a bit like a chicken and egg problem - why build all the silicon to handle decoding it if your base ISA is dense enough?
(IIRC they removed that one on x86-64)
RISC-V compact instructions don't require special modes and run in fully-mixed mode with 32-bit instructions without all the penalties thumb has (they are literally just extended into their 32-bit counterparts internally).
High code density became less valuable, was the point.