I understand your myopia. Soccer moms who voted for Bush would NOT vote for him a second time if he broke his promise to support existing gun laws.
The soccer moms who vote heavily on the gun-control issue and who voted for Gore because he tongue-sucked his wife on national TV will not be voting for Bush even were he to ban all guns outright.
There is no upside to Bush's maintaining this "promise". He is doing so because he must honestly believe black guns are evil and have no place in modern America. And I don't see how that squares with the Constitution or with his perception as nominating jurists who have a stricter interpretation of the Constitution. I mean, Ashcroft appears to be pro-RKBA to a greater extent, but what comes from Bush's mouth is not so impressive.
I will vote for him anyway as I have no choice. Any Democrat would be worse on RKBA.