Though the best mathematicians have chewed on the problem for hundreds of years, there just doesn’t seem to be any way to factor large numbers efficiently.
That fact makes primes vitally important to communications. Most modern computer cryptography works by using the prime factors of large numbers. The large number that was used to encrypt a file can be publicly known and available, because the encryption works so only the prime factors of that large number can be used to decrypt it again. Though finding those factors is technically only a matter of time, it’s a matter of so much time that we say it cannot be done. A modern super-computer could chew on a 256-bit factorization problem for longer than the current age of the universe, and still not get the answer.