These usually get planned well in advance by some very sick people who are trying to kill as many people as they can and go out in a blaze of glory. Sure, the existence of opportunistic terrorists networks that get these people to coordinate their attacks and stamp a ideology on them tends to mean that the one day body count is higher for a particular incident. Still, the body count per attacker is often comparable, it's just that the attacks happen on the same day instead of a few weeks apart.
But yeah, if we ignore the non-Muslims who do things like this we can say it's all the fault of Muslims.
Still, people don't find it inappropriate to bring up Columbine when they talk about VTech or Aurora. When people try very hard to exclude all the other mass attacks and single out only the ones connected to Islam in situations like this speaks more to their personal biases than anything else.