Can be explained with the mathematical properties of multiplication:

1.Identity property of multiplication:

The number 1 is the multiplicative identity, meaning any number multiplied by 1 remains unchanged:

X times 1 = X, for any X

If X=1, 1 times 1 = 1

2.Commutative property: Order does not matter in multiplication:

A times B = B times A

Thus 1 times 1 = 1

There’s also the conceptual reasoning:

Multiplication is essentially repeated addition: when you multiply 1 by 1, it basically means add 1 to itself only once, which is just 1