The thing is to define what you are protecting against whom.
In the case with blurring license plates, I may want to protect my online identity vidarlo against any correlation with name and address. Blurring the license plate of my car (I don't own a car, nor do I hide my identity, but...) when I post pictures of it online makes it more difficult to find my identity and location.
If you have the plate, it's a matter of a lookup in a public registry. If you don't, you'll have to recognize the car or location specifically, and the location may be publicly accessible.
The cost of blurring is low, and it's effective against a specific type of attack.
The no fly list attempts to stop people who may hijack planes from getting on planes. This is a more difficult problem, as it's largely unknown who will attempt to hijack a plane - and wanna-be hijackers can test the security by attempting to fly with no ill intent. It's costly to maintain the list, and it's costly to individuals who are on the list by mistake. In fact, it's so difficult to maintain that USA doesn't manage to.
In addition, it's the problem of false positives. If you're not interested in finding my identity, it likely doesn't bother you a lot that the plate is blurred. The cost of false positives is effectively zero; I don't need to discriminate between attackers and non-attackers.
As for the no fly list
Imagine you have a test that is 99.999% accurate - it will identify terrorists with 99.999% accuracy, and the false positive rate is similar.
Now, last year there was 4.3 billion airline passengers. Imagine that 100 of them was terrorists. If you run that 99.999% accurate test on all passengers, it'll give you 430000 names. Of those, 100 are terrorists. The wast majority are false positives. Checking those 430k people will be a huge job.
And 99.999% accurate is probably overly optimistic. This makes it very difficult to make a usable and useful list.