Hey there,
The reason behind this, according to him, is that people are more willing to donate if the donation amount is no longer at 0 so, starting already with a small partial amount could potentially make people more likely to buy your bundle and help you profit from your sale.
I would imagine this is exactly why this might not be implemented. People would just put random amounts, in an effort to make their game look like they are doing better than what they actually are, and it might results in nobody trusting the numbers.
Having said that, this is up to the admins to decide.