If your system (pseudo-) random number generator (RNG) is compromised to derive a portion of its entropy from things that are knowable by knowing the time when the function ran, then the search space for cracking keys created around the same time can be shrunken considerably.

This doesn’t even rely on your system’s built-in RNG being low quality. It could be audited and known to avoid such issues but you could have a compromised compiler or OS that injects a doctored RNG.