Same reasons most people consider it bad: you're not taking a shot at mafia, you kind of kill discussion if no one is under threat, and you'll (probably) never have a point in the game where it's safer to lynch (well, unless you lynch a mafia day one and the doc manages to save night one. Then I guess lynch on day 2 is even safer since you've gained ground). The downsides to a bad lynch are much less now than they would be later basically.

I guess I could see how trying to limit the town deaths to one on day one might be desirable, but I'm generally against plays that are safe for the sake of being safe. If it's do or die and the safe play is actually the best option then sure, but not right now.