Because we need less protection from the government of today than people did from the government at the time the laws were written :ermm:
Are you serious?
Back in the 1700s, it may have been possible to resist the government because the government had the same guns people had.
In the 21st century, you are 100% dead because the power balance has shifted so much in favor of the government.
Precisely because of the power imbalance, and because of the changes in both technology and society that have happened meanwhile, that argument (if it ever was valid) does not any more outweigh the negative consequences of everybody having guns.
Japan has 40% of the population of the US, it records about a dozen gun violence deaths a year, in the US several hundreds die every year just from guns firing accidentally. and about ten thousand in total...
It's hard to argue with that stastic.
Meanwhile, big business has bought the government and has quite successfully created a corporate police state. Somehow people having guns has not prevented that. Not only that, but it is the people who are most keen to have guns that have supported that transition...