A knee-jerk reaction
When a tragedy occurs people want something done, as long as it does not affect them. This often results in a knee-jerk reaction against innocent people who are made to pay for the crime of a perpetrator. A case in point is the recent tragedy in New Zealand which, like a similar case in Australia in 1996, brought the wrath the government on law-abiding citizens, with clamping down on gun ownership by sporting shooters, even though the perpetrator back then was unlicensed and used an unregistered gun, and in the recent case the perpetrator was not legally entitled to have the guns that he used. Such laws will do nothing to stop criminals or terrorists from getting illegal guns, which are freely available in both countries.
If other weapons are used, such as cars running into crowds of people, there is never a call to restrict car ownership, because that would also affect the people calling for action. This is hypocrisy.