If current time in milliseconds is considered good enough random seed for a pseudorandom number generator, why not just use that time directly?
The key property that we want from (non-cryptographic) pseudorandom numbers is that they "look" independent. In particular, say you have some algorithm that requires a PRNG to perform well and you give it a current time function as a PRNG. Then, if the algorithm repeatedly queries what is supposed to be a PRNG, it will actually see that it gets the same value many times in a row until, until it eventually increments by one. These values are very, very far from random and can be detrimental to algorithmic performance.