Depending on the context, you can almost always replace "Why reinvent the wheel?" with "Please don't compete with me," or "Please don't make me learn something new." Either way, the opponent doesn't have a real argument against building something newer and better, but they also don't want to admit their unhealthy motivations for trying to stop you.
More seeds, more blooms, I say. Don't build houses on kitchen sinks. Reinvent away. Most of our current technology sucks, and even if it didn't, who am I to try and stop you?