Efforts to interrupt terrorist financing have been successful when it comes to large amounts of money, but much less effective in stopping the money needed to pay for your average terror attack. Multi-million dollar chunks of money were needed when al Qaeda was trying to establish bases in places like Sudan and Afghanistan. But since September 11, 2001, al Qaeda has no place where it can spend a lot of money to establish bases for training and support for terrorist operations. The attacks that have taken place in the last few years year have not required much cash. Most attacks require no more than $10,000-$20,000. Amounts this size can often be raised locally, or sent, undetected, via courier or informal wire transfer (the ancient Hawala system used by Arab migrants to send money home.) 

Large amounts can still be transferred, using the illegal money laundering network that services criminal operations. Since there are many Arabs involved in money laundering, and a no questions asked atmosphere prevails, terrorists can, with some risk, move lots of money this way. There is risk, as the money laundering networks are under constant attack from police organizations world wide. The word is out that nothing but lots more trouble will happen if money launderers are found with terrorists as clients. The reason for this kind of pressure is that, one thing terrorists would move large quantities of cash for is the purchase of nuclear weapons, or ships to be used for large scale attacks on ports. 

The Hawala networks have taken a beating as well, although in some countries they have been allowed to continue operating, in return for providing information on what money is going from who to where. Criminals in general now know that rewards are widely available for any information on terrorist operations. Just the knowledge that this is the case is a weapon. Terrorists have to be even more careful, and thus slower, because of the increased risk of informers. Most criminals, even Moslem ones, feel free to inform on terrorists. Crime is a business, and terrorism tends to put everyone, even Moslem criminals, at risk. The more civilians, and Moslems, terrorists kill, the easier it is for gangsters to justify ratting out terrorists. Under these conditions, dealing with terrorists makes you liable to getting prosecuted as one if caught helping out just doing your usual gangster gig. Meanwhile, providing information on terrorists gets you some kind of reward, even it is just some lenient treatment the next time you get busted. 

Making it more difficult for terrorist supporters (including a lot of charities) to send money to terrorists simply drives the terrorists to rely on criminal networks. Here is where rewards (of cash, or lenient prosecution) keep the pressure on. You can never completely shut down terrorist money transfers, but you can make it a lot more difficult and dangerous.