Brian Thompson was more widely hated.

Not only that, but Thompson's death wasn't seen as overtly political by the public. If Kirk's shooter, for example, turned out to be someone that lost a family member in a mass-shooting, their actions is going to be relatable to the public - just like Luigi's action was. But if the shooter just turns out to be somebody trying to make a political point... well, we all know how that's going to turn out.

This is the problem with these high stakes PotD games... they backfire real easy, and a lot of the people willing to do it are also the people that seem to understand that the least.