I agree that we should be disavowing violence.
The problem is that for 10 years democratic lawmakers and media figures are disavowing violence on both sides, while republican lawmakers and media figures are doing the opposite: stoking the flames, promoting the idea of civil war, telling everyone that the country is stolen from them, that immigrants are out to get them, that democrats are out to get them, etc. According to this rhetoric, democrats are to blame for all of this. When something bad happens and it's not democrats who caused it, they come up with a conspiratorial explanation for how it's still democrats.
So when one side keeps constantly disavowing, and the other side keeps constantly attacking, at some point disavowing becomes literally the wrong thing to do. You can't lay down your weapon while the other person just keeps hitting, and expect the hitting to stop.
What we are being shown repeatedly by republicans is that violent, divisive rhetoric actually leads to electoral victories, and grants free license to become "president for one side only" and do whatever that side wants. If democrats continue to disavow and apologize, they will end up simply extinct. This is why some democrats stopped doing that.