It becomes more natural/C-like if you think of

    ADD foo bar

not as

    foo + bar

but as

    foo += bar

And then apply a prefix syntax correction, to end up with

    += foo bar

(Or, equivalently, always mentally add the word "TO" to each operator that modifies an argument, which is most)

Also, most intel instructions use one or two arguments as input, and modify one of them as output. It sort of makes sense to have the output (or input/output) argument always be in the same position, regardless of whether an instruction takes 1 or 2 args. BTW, even in riscv where "add" takes three args, i.e. the form is a = b + c, the output-only argument a comes first.