They’re jealous that someone with an iPhone and an app can shoot a better photo than they can. I’ve visited hundreds of so called “Pro” photography portfolio sites, and there is a larger than average amount of just crap on those sites. It’s not Instagram’s fault your exposures suck, or that your composition sucks, or your subject sucks, your lighting is off, and most importantly, that your photo doesn’t tell a good story.
iPhones are accessible to everyone in a way DSLRs are not, and in the right hands can shoot a photo that rivals or even surpasses anything a DSLR can do. No MASP, no adjusting ISO, no adjusting Exposure, just point and shoot. They’re small effective little fuckers that scare the crap out of photographers like me.
The problem is photographers just get old fashioned jealous when they think someone is cheating with an app, or that using an iPhone isn’t real photography. Shooting pictures with an iPhone is just as real, and just as relevant, as shooting on any other format.