Unless I'm forgetting something, 9/11 involved planes crashing into large buildings. Most movie theaters in the US are single-story buildings and seldom have much around them of great significance (ie they are in big empty suburban parking lots). They would have to completely destroy dozens of theatres in order to match the death total of 9/11, and in the process wouldn't come close to the monetary damage.
But that leaves the giant question of how. You can't take down a full movie theatre with one suicide bomber, you would need several (at least one for each screen, somehow synchronized to maximize damage). 9/11 was 19 terrorists killing almost 3,000 others; you can't get anywhere near that level of destruction with suicide bombers.