Assembly mnemonics I think are terse to make it dirt simple for assemblers to read them, which themselves had to be hand-entered via hex until they became "self-hosting." Assemblers could not be on the same level as compilers. This was definitely very needed when these CPUs were new in the 70's and such.

I've always liked how 6502 neatly has everything in 3 letter opcodes. But that's not scalable given modern CPU capabilities.