I could just as easily say: There is insufficient support for it across the US. Democrat Congress members and Senate members, many of whom receive campaign funding from the anti-gun groups, continually fail to gain enough support to make changes.
The U.S. is a constitutional republic, not everything needs to be done at the federal level, state laws exist and the Second Amendment could be completely removed if enough states want it gone, but they don't.
Give it some time.
The first generation of school survivors* will start to be getting old enough to run for higher offices in the next few years...
The US has spent the last 20+ years with a lot of it's politicians deciding that the murder of hundreds of school children is worth while, and traumatising millions more** with regular shooting drills is nothing unusual, whilst those children in question are are growing up with the ability to see that what they're forced to go through is something that is unique in the western world to the US, and only seen to lesser degrees in third world countries without functioning governments usually where the extremists don't want children to be educated.
Someone I saw a few weeks back made a very good point, most adults in the US especially the current politicians have no idea of what it's actually like in the schools, or the sort of things that preteens are being expected to decide on, let alone the teachers, things like which child is going to get to go in the supply closet, which one is going to be designated to run over and put stuff over the windows to prevent a shooter seeing in, but also making themselves a prime target. Apparently the kids don't tell their parents even about things like false alarms a lot of the time (and the schools don't necessarily inform the parents), as it's "normal".
It's also worth noting, as others have said the majority of US people when polled, including gun owners are supportive of at least some basic "gun control" laws it's the Fox news viewers and the borderline nuts who can't distinguish between say stopping someone from buying a gun on a whim and using it to kill people (especially those who are known to be high risk, such as people with restraining orders for domestic violence) and taking all of everyone's guns away...
I mean they go on about "yeah well what about illegal guns", but then don't want the government to know where those illegal guns are coming from or have any ability to reduce how many illegal guns there are (by for example having a registry of reported lost and stolen weapons, or requiring that you take more care of where you leave your guns than your TV remote).
*I remember when "surviving high school" was sort of a joke, now it's a real thing in the US.
**There has from memory been a marked increase in the number of children and young adults who are being diagnosed with PTSD type issues, because for the last 20 years they're ended up being taught that basically any loud bang in a school could be a shooter, and trained to hide under their desks both in drills and in scares.