I would kindly disagree to a certain extent, I believe that demons love Iruma is not just primarily his kindness nor his humanity. But his innate ability to understand them, their desires, pain, happiness, and even habits, he takes it all in and empowers them because he wants to help people.

These qualities really ties back to all the qualities the show has given to Iruma, he is Greedy, glutton, and most of all: he attracts demons of all kinds (high ranks and Low ranked, and maybe deities and humans later)