1. Because I have zero reason to take his word for anything he claims. The authenticity and veracity of the video, on the otherhand, isn't even in dispute and there's no reason it should be.
2. Because the object in the video is headed northwest, as revealed by the sunlight. Just like the camerman said (though the cameraman actually said it was headed west, but he also said it looked inbound, and as he was in Santa Monica -- you ARE familiar with the L.A. coastline, correct? -- it would look as if it was inbound if it was headed northwest).
Of course the video is in question. Where is the full footage? I don't criticise the TV station. Obviously people would become bored if they had to sit through the full footage, but it is edited for effect.
If they have nothing to hide then they should release every portion of it. CBS should have provided full copies of the footage to all parties that they interviewed. They should also be sending all the footage to the likes of Jane's Rockets and Missiles if they are so positive that this is a missile. The LAX web cam images prove that it headed inbound. Rick's images also prove that but you have dismissed them simply because it doesn't fit with your missile theory. Correct?
Also consider that the portion where the claimed rocket boost is has also been slowed down for dramatic effect? All you are seeing is edited video that resembles a ballistic launch. Even Jane' Rockets and Missiles have dumped their initial missile quote after seeing the later footage after the persistent contrail.
Why do you dismiss Rick Warren's images when the later portions of the CBS video show the object in the same perspective as Rick Warren's images? Rick was 10 stories up and obviously the helo was at height.
Watch the video from 0:45 section. This is why Jane's Rockets and Missiles are no longer calling it missile footage
Even just before the 0:45 point you can see the object (my take airliner) cease it's persistent contrail and continue with a non-persistent contrail. The MD-11 at this point would be up at around 39,000 feet.
Based on your observations these two aircraft contrails would also be ballistic missiles? Perspective and edited video have fooled observers of this MD-11 plain and simple.
December 2009 California footage
Aircraft example from 2008 - Florida