Thumb works as an alternative encoding that you have to switch to and where you just have a subset of the instructions available. Switching has at least the sam

Thumb works as an alternative encoding that you have to switch to and where you just have a subset of the instructions available. Switching has at least the same cost as a branch. My guess is that this is the reason why thumb is avoided often. RISC-V on the other hand has an encoding scheme that already from the beginning allowed instructions with longer and shorter encodings. You can just mix compressed instructions with normal ones.