3 is a prime, 5 is a prime, and 7 is a prime. Why bother with non-prime numbers when the primes can do everything?

Simpler explanations are, other things being equal, generally better than more complex ones.

Of two equivalent theories or explanations, all other things being equal, the simpler one is to be preferred.

Plurality is not to be posited without necessity.

Whenever two hypotheses cover the facts, use the simpler of the two.

When you have two competing theories that make exactly the same predictions, the simpler one is the better.

The explanation requiring the fewest assumptions is most likely to be correct.