A good question with a simple answer. Since "tougher gun laws" will not stop such killings, the cries will never cease as long as guns are available at all.
IOW, gun laws can never be tough enough. Any gun crime will result in calls for tougher laws, no matter how tough they already are.
.....Or they want a tougher law so that it lands up in a fed court, most likely the USSC as a test case.
We should ditch the laws altogether. A shooter is going to get a gun and use it no matter what the law says. Its foolish to believe a law stops anyone from committing a crime.
So called “reasonable” gun laws are reasonably stupid.