Toad actually stored that value, so the next time you went in, then it would display that default value again.
But, in reality, that default value could actually be changed, and then if you used Toad, then it would be defaulting the old value instead of the new one. This way is actually better because it prevents an issue if someone changes the default value.
Another point is that the default value is not needed in the anonymous block. It will run without that variable because it's a default value.
It was seen copying that anonymous block and run it somewhere else, but even then it's not needed.
But if one really want it there, then one can change the "Input Type" to Default/Literal and that will put it back in there.