Yes, because people have access to mass murder weapons.
People can not actually murder in masses outside of serial killing which requires finesse and secrecy.
US likes to blame mental illness, as if US is the only nation with severe mental illness.
Do we need to start another debate as to how other countries are much better with mass murder statistics compared to US?
One might argue, why California or Chicago does so poorly even with its strict laws, but the answer is simple. If it cant control its borders as to how weapons enter the legislated areas, then those laws are futile. However, countries that can control its borders and control that actual weapons within have much better success at doing so.