The simplest answer is the fact that right to bear arms is in the Bills of rights and part of the constitution it would require a 2/3 vote on house & senate to change the amendment. That vote would never happen. Which leads to the other main issue in that the reading of the second amendment is open for interpretation. Some noteable rulings on gun rights are McDonald & Heller (2008). In both cases the justices interpreted the reading of the law to extend gun rights. With a conservative Supreme Court presently in place, there is no way things are changing soon.
I would also point out that privilege and wealth come into play. Even democrats don’t truly care to change the laws. Public schools are getting shot up, not where their kids are. Middle class and lower class neighborhoods are where many mass shootings happen. It’s an apathy because it doesn’t effect the elite who are the political donors, the CEOs, the ones being the lobby groups. And until their money is effected, politicians do not care.
despite the majority of Democrats and the party itself being pro gun control, the wealthy elite of the Democrats still tend to be the good-ole-boys (white, older men) and they still want their guns.