Coming to what you asked-Prime Factorization essentially implies writing a number as a product of its prime factors only.

If we say 25 can be written as 2^0 *5^2 (with 2^0=1)we are implying that 25 can be written as not only 2^0*5^2 but as a product of any prime number(s) like 3/7..etc(that are not present in the factorization of 25) raised to the power 0(3^0/7^0/etc) and multiplied with a 5^2 as well!! This would lead to an infinite representation.

A prime number not present in the prime factorization of the number is represented by a^0.

Thus, power of 0 is not used to represent the prime factorization of a number.