Al Qaeda never made sense, according to Gary Brecher (The War Nerd):
The whole concept of Al Qaeda is wrong. The name means “The Base” in Arabic, and the idea is that it’s a central clearinghouse for dozens of different guerrilla groups, sharing an Islamic ideology but representing different countries and tribes and languages. They get together and share intelligence and personnel and materiel, because they’re all good Muslims working for a common cause. It’s the old kiddie dream of a vast umbrella group of baddies, S.P.E.C.T.R.E from Man from Uncle, KAOS in Get Smart, the ridiculous villain and his volcano HQ in every lame Bond film.
It’s just a terrible idea. The last thing any sane guerrilla group wants to do is to go to an international guerrilla jamboree like the Boy Scouts. Sure, you’ll share ideas and prop up each others’ morale—and in the meantime, the informers—because every decent-sized guerrilla group must assume it’s been penetrated—will be taking careful notes, taking quiet candid pictures, and putting together organizational charts. By the time you go to your home country from the big Jihad Jamboree in Waziristan or Tora Bora, you can be sure that the informers have shared their info with their handlers. And although some intel agencies can be stingy, most of them share info very readily, so every informer has in effect given the breakdown of every local group to every intel agency in the world.
And that’s death to a guerrilla, literally death, and not a quick or easy death either. Sharing info is good for intelligence agencies (most of the time; there are exceptions, like sharing the identity of some agents), but it’s the worst thing in the world for guerrillas.
That’s why guerrilla groups either start out with or switch to cell style organizations. Many times you’ll see a guerrilla group starting out imitating military organization, with big units and uniforms and parades. That’s asking to be wiped out. Sometimes they are wiped out; but if they survive, their second coming always involves switching to four-person cells, where three out of four members don’t know anything except the identity of the other cell members. And even the fourth, the cell leader, only knows the identity of one contact in the larger organization.
By bringing Jihadis from around the world to get Osama’s blessing, Al Qaeda was giving them a short-term boost in morale and finances but pretty much guaranteeing they’d be penetrated and destroyed within a few years. And that’s what happened: a big splash on 9/11, a few aftershocks in East Africa, Bali, Madrid and London, and then nothing but cops breaking down doors all over the world to the soundtrack of Hellfire missiles from Predator drones vaporizing mud houses in Northern Pakistan.
What made Al Qaeda so scary was that they went all out, in an age where the military norm is to use a tiny little fraction of your actual power. To see that style in action, just look at Libya now: NATO has the largest common air force in the world and could make every Qaddafi-held town in Libya a column of black smoke in a few minutes, but what they actually do is hold a classic EU discussion before taking out a single tank.
Al Qaeda made its mark by using everything they had. Every contact in every country. Every dime of finance. Every pound of plastique. Every willing suicide bomber. They literally doubled up on their attacks, trying for at least two big targets every time: the WTC, Pentagon and White House on 9/11, multiple tube stations on 7/7, two Israeli vacation spots and a US Embassy in Kenya. That sort of splurging really shocked bureaucrats who’ve spent their lives hedging their bets. And it worked, short-term; it made Al Qaeda look much bigger and more important than it really was. For that matter, the only reason they lasted as long as they did is that Western intel didn’t have any decent Arabic-speaking specialists.