No move instruction

Is there a reason for not having a move instruction in the mipsasmgen package?

Of course we can avoid move, e. g. or $t1 $t2 $zero instead of move $t1 $t2, but it seems kind of weird as MIPS already provides us with the move instruction.

The reason is that move is a pseudo-instruction. As you have seen, there are several equivalent instructions which you can use instead.