Sure, there have been 4 incidents where non-crew members destroyed a plane in flight departing from a US airport since 1961. They were in 1961, 1962, 1987 and 2001. So if you work out the rate of such attacks before the TSA (including the 2001 attacks), that is 4 per 40 years, or about 1 per 10 years.
Given that frequency, it is not that improbable that 16 years might elapse without such an attack. (One can work that out more precisely of course, but I think one can see that it is not that unlikely for 1.6 10 year periods to go by without an attack when one only expects 1 per 10 year period).
Thus the argument that the TSA works since there have been no attacks since 2001 is, statistically speaking, invalid.
Given the lack of good evidence that the TSA works, and plenty of other evidence to suggest their procedures are not effective, spending $8.1 billion per year on this "security theatre" seems a very severe mis-allocation of resources. If one wants to spend that kind of money on saving lives, there are likely 100X more effective ways to spend it.