Zombie movies exist because people wanted to make natural disaster movies where you could delay or speed up the disaster whenever the plot called for it, without ruining suspension of disbelief, and in Sharknado, shooting the tornado looked stupid, so it's just easier to shoot zombies.

Zombie movie plot points and hurricane movie plot points are the exact same: Everyone's happy, suddenly bad stuff happens, gotta get medical supplies, someone was injured in a way we can't heal so we gotta euthanize them, main leads have romantic subplot.