How hard is it to explain to people that their vote only goes to #2 if #1 is already out of the running?
And besides, it’s really not fair to assume that voting systems are simple to understand. Just have a look at https://en.wikipedia.org/wiki/Comparison_of_electoral_system...
I agree there are other methods that are better by the book than the IRV method, but are exercises in statistics and graph theory.