See, the Salafists aim is to apply Islam, no more and, most definitely, no less
But wouldn't most Muslims agree with that? Every sincere Muslim would presumably want to be a good Muslim. The controversy seems to arise over that Islam is in this context, what image of Islam needs to be "applied", how it's to be applied, and to what.
The Salafists seem to me (I'm not an expert on this) to favor a very literalistic and traditional application of Islamic law and jurisprudence, applied to society as a whole, and to all the many diverse individuals within that society, by force if need be.
Salafism isn't an invention, it's essentially Islam.
My opinion is that all religions are inventions, human inventions at that.
But leaving that issue aside, the equation of Salafism and Islam is also extremely doubtful in my opinion. Salafism in the Islamic context is something like Puritanism in the Christian Protestant context. It's not unlike the 15'th and 16'th century dreams of establishing a 'Biblical commonwealth', the dream of reforming all of society into a God-fearing community in keeping with what was believed to have been God's revealed will and the idealized faith of the earliest community. It's a manifestation of nostalgia for an older medieval sensibility, and a contemporary reaction against the world-wide march of modernity.
Their doctrine is to apply the instructions of Islam and what's deemed true of the prophet's teachings. Which is precisely what Islam instructs. So the backwardness you speak of isn't because the Salafists chose to make certain rules, they are simply applying the instructions of the Koran and Sunnah.
Interpreted as law, analogous to the existing secular law of the 7'th century, but revealed this time (supposedly) by God himself, and hence binding on the community (and ideally upon the whole world) for all time. That kind of belief threatens to trap the Islamic community in a medieval sensibility forever.
Meanwhile, millions of Muslims have been moving geographically to non-Islamic lands, and then struggling with the sometimes uncomfortable necessity of transforming themselves psychologically, coming to terms with being minority individuals in highly-diverse societies that aren't defined by Islamic law and aren't organized on Islamic principles.
Islam is going to have to find a way to become a personal religion, a religion of individuals and not of entire societies. Some of the Sufi tendencies in Islam might represent resources existing within Islam itself that might be of help.
So what you should wonder about isn't Salafis, it's Islam. You should ask why is Islam a threat to the progress in the region ? Why does Islam want a backward society ?
I don't agree with your equation of Islam and Salafism.
Why is this kind of religiosity increasingly popular among Muslims? Probably because many Muslims feel increasingly on the defensive against the globalizing changes sweeping the world, against modernity, which they sense is antithetical to their own traditions and is being imposed on them by foreigners from outside. They want to stand strong, shoulder-to-shoulder against the threat.
They don't perceive their traditions as being backward or as a threat to progress. Quite the opposite, they see an ostentatious return to their own early medieval traditions as being their path back to power, to the invincible strength and divinely-willed inevitability with which Islam originally spread across half the world in the early Islamic centuries. The way to that reformation is to sweep away what they perceive as their own culture's decadence and impiety.