Humiliation
The summoners still weren't so fond of Bardeelus. They didn't consider him a hero, and come to think of it, they were barely thankful towards the town of Artakam as well.
These summoners were surrounded by their monsters, and had summoned many other physical stuff prior to these monsters. Results like those helped boost one's ego.
Such ego left them unimpressed with most other things. They didn't care about a 'smart fella' who worked and guided people from the shadows. Half of these summoners were teenagers, even, so their arrogance was beyond humane bounds.
"So you're the pure one? What do you do all day, tickle bones or something?" One of them asked.
The questions didn't stop there, as another one joked. "Did you ever hump one of your slaves? We caught Feran doing that."