Trying to literally make one commit every day (as opposed to something like seven commits every week) ties one to a schedule that would be unrealistic for many people. I enjoy activities like backpacking, international travel, and spending entire days with my girlfriend; none of those are very compatible with a goal of making one commit in each 24-hour period.

It also seems extremely vulnerable to the "what the hell" effect. Miss one day, and you've technically blown the goal. Worse, the reason for missing a day may be largely out of your control (illness, power outage, blown CPU, whatever); unless you have a solid "when (not if) I fail..." plan, you may find yourself choosing not to push as hard to fix things because "it's not my fault".