Generating random tokens is cryptography. It just happens to be done more by non-cryptographers, which doesn't necessarily mean they're better at it (hint: they aren't).

You can perform cryptanalysis on random tokens and if the RNG (or PRNG) isn't seeded properly, you get a replay attack. This is not to mention: aside from attacks, you have further crypto to do aside from the generation: how do you verify the token?

If you roll your own RNG/PRNG and token generation, it is probably just as broken as the block cipher you tried to roll yourself as well. Using standard libraries and well-audited tools brings ciphertext authentication into the same realm of usability for developers that token generation is in.