One advantage of a simpler/more regular ISA is that it's easier to maintain the tools (compilers, bits of assembly in low-level libraries / OS kernels etc) whic

One advantage of a simpler/more regular ISA is that it's easier to maintain the tools (compilers, bits of assembly in low-level libraries / OS kernels etc) which enable you to avoid writing your software in assembly. Read: easier for software tools to write the assembly code for you.