I don’t understand why this idea angers people.

I think it’s the arrogance of thinking that your experience is the norm. A great deal of people who rent have shitty landlords who will only do the very bare minimum of maintenance and only begrudgingly at that. And most people who have a house with a mortgage have much lower expense than those who rent. Mostly due to the fact that mortgages stay the same over the time you are paying them and then they go away once you’ve paid them off and (unless you are lucky enough to be rent controlled) rent usually continually goes up yearly or bi-yearly.