Multiplying means adding a number to itself n times. Adding zero times means nothing is added, so the result is always zero.

If you have 5 baskets with 0 apples each, you have 0 apples in total. Any number of empty groups equals zero!

If you have 5 boxes with 0 cupcakes in each box, then 5 × 0 = 0 cupcakes in total.