Simplest answers likely the correct ones. Either the opportunity to attempt assassination isn’t there in quiet security seclusion so n the perp must take what opportunity t gey have which may be noisy x and busy, and the noise and busyness of a crowd may help the killer to attempt escape in the mass confusion.
Currently, it’s easiest to have the greatest impact in the public mind if there is dramatic, gory film to show over and over and over again.