The politics landscape has changed quite a lot. What changed is that gun companies lobbies lobbied the government and bought a bunch of politicians on both sides of the aisle and they continue to lobby to this day.
They also made a big push to convince the general population that guns are necessary for home defense, hunting, personal defense/security, and other recreation. And played up those factors to the part of the population that wants to gravy seal it up.
Further, there's an increasing lack of bipartisan support for most legislation (not just gun law). A lot has changed.
In order to change an amendment you need to take a couple of steps.
One of these is getting either a 2/3 of states to call for a constitutional convention or for 2/3 of both and Senate to agree to ratify the amendment. So I think if you look at the political landscape of today you can certainly understand why it hasn't happened.