I think communications technology has a lot to do with it too. Pre-the collapse of the Soviet Union, fighters such as ISIS (Al Qaeda, al-Aqsa, ect and so forth) remained isolated from the rest of the world. Knowledge of them and their agendas didn't spread to the degree it does now. So while enhanced communications technology has lots of benefits (see: Police/Citizen relations in the US) it also empowers everyone to create global identities. When the Mujaheddin were fighting the Soviets for Afghanistan, those fighters were forced to rely on nations to tip the balance when conventional sources of support were not enough. They couldn't turn to the rest of the world en masse for support. They couldn't organize fighters as quickly or efficiently.
Now, every extremist group has a website. They recruit online. They post on Twitter. They network. As fucked up as it is, in an academic sense I'd be interested to know what an extremist group Kickstarter could bring in. (Which will never happen because of Kickstarter policies.)
Subsequently, in the course of doing their jobs (poorly), the media picks up on their "brand" and reports on it, and elevates them in all our consciousnesses, bestowing recognition and, for lack of a better term, legitimacy on them. Sometimes that should happen, when real issues are being under-reported. But a lot of the time it's a mixed bag of pros and cons at best. I really hate the beheading news stories in the American media for this reason. So lucky for the media that it is both sensational and important, so they get the best of the both worlds while essentially giving extremists exactly what they need. Despite the internet, not everyone would pick up on a video of a beheading in the course of their normal lives. But when the American media picks it up, there is basically no way of avoiding it for the average citizen.