I also wanted to make another point. I work with Nile monitors, and they do get big and nasty, but they are NOT cat hunters. Obviously a cat would stand no chance against a Nile monitor, but a Nile monitor simply would not actively hunt cats. Obviously if it's starving its gonna. But the fact remains that these lizards are scavengers.

I am willing to guarantee that 90% of people who "see" a monitor eating a large mammal such as cat dog racoon possum etc. Are actually witnessing the lizard scavenging for prefilled food such as roadkill or things that have just passed away. In they're natural habitat they scavenge almost all their food. They are NOT going to evolve into stalking predators in florida.