just because they have money doesn't mean they can simply do it. It takes deep connection and expertise to pull it off.
What makes you think they don't have deep connections and expertise, in addition to money? (Don't forget, money can buy lots of expertise and connections, too.)
...flight schedules. immigration/passport paperwork. commercial flight training. communication & coordination. massive funds and moving funds around (not easy).
Prior to 9/11, getting passport and immigration documents didn't require sophistication. Even now, our borders leak like a sieve.
Many potential terrorists can easily show up on student visas.
Moving funds around is no big deal (anyone from Jersey should know that, heh, heh).
Prior to 9/11, no one thought twice about the flight training. It wasn't restricted, and didn't require sneaking into.
Side note:
Prior to the revolution in Iran, we trained their fighter pilots on our Navy bases in America, and their military officers in our upper level training facilities. Obviously they didn't "forget" all that training when the Shah was given the boot.
It's not that hard for terrorists to find trainers. For the right price, you can find rogue experts in anything.
All above.... and the CIA, FBI, Interpol, etc. didn't catch a hint of it? bullshit.
They DID catch hints of the planning; they just didn't put it together and disseminate it properly.