CPU instructions like load and move can apply an offset that is encoded as part of the instruction. This is more flexible than a special instruction for "offset=1", and useful beyond 1-based indexing. See for example https://www.cs.virginia.edu/~evans/cs216/guides/x86.html and https://www.keil.com/support/man/docs/armasm/armasm_dom13612... .

I'm not sure about "multiply and add"... Aren't these instructions for computing with floating point numbers rather than offsets?