And if you're generating your one time pads using a (hopefully cryptographically-secure) pseudorandom number generator, then congratulations! You are literally reinventing a stream cipher except with enormous, non-reusable keys.
and enormous keys too! you might need to store them on some sort of notebook or large paper thingie!
By using a PRNG (even if it is a cryptographic stream cipher) to generate your pad, you've just re-introduced the same "crackability" (by way of the PRNG), and your system is strictly worse (same security, worse logistics) than an existing system.