Text do not stick to camera tracker - why?

I see a couple of errors in your workflow. The first mistake is that the tutorial you linked to was made by an amateur that kind of figured out a way to make something work but left out a couple of key steps in the process and also demonstrated a completely amateurish way to create a shadow that was not even closely lined up with the rest of the shadows in the shot. You have to vet your trainers.

The second mistake was completely procedural. It is important to set an origin and ground plane and stick some kind of a reference object, text or solid to the ground to see if it tracks properly. The option is near the bottom of the panel that opens up when you right click on a target. A better technique would have been to set your target as the origin and ground plane, then create a solid or a text and camera and check the tracking. If it sticks you then can start manipulating the placed 3D element.

And even better technique would be to size the target before you place your text layer so that the size is appropriate. It is also not a good idea to use Scale to resize text especially when it is a 3D layer because Z scale is also changed and this can move the text if the anchor point is not precisely on the z plane. Sizing the target helps get things the right size and using font size is also a good idea.

If your placed 3D layer is snot tracking you should first open up a second 3D view and see if the placement makes sense and the camera is moving as it should. If you established an origin and ground plane and placed a reference there the object should be at comp center. If you did not the placed 3D layer can be anywhere.

Another thing that may be throwing off your track is the lens distortion in your shot. There is quite a bit of lens barrel distortion in the shot. Notice the curved horizon:

The AE camera is perfect. If your shot is not it's a good idea to fix the distortion before running a camera track. Sometimes fiddling with the knobs in the camera tracker can give you a more accurate solution.

So here's what I would try. Pick several tracking markers somewhere in the middle of the shot to get a target that looks like it's pretty well lined up with the ground, Size the target so that it looks like it is about the same size as something in the shot that you can use to line up a ground plane. set Origin and Ground Plane and then add a solid and a camera. Now add Effects>Generate Grid to the solid and see if the grid lines up with the ground. Check to see if it sticks to the ground. If it does you can replace the solid with a text layer or just create a new text layer, make it 3D, select the placed solid, hold down the shift key and parent the 3D text layer to the solid. This will snap the 3D text layer to the exact position and orientation of your test solid.

If you can't get the solid to stick to the ground then your track is no good and you'll have to make some adjustments to the camera tracker settings or remove the lens distortion and start again.

last point - make sure that Active Camera is selected and the comp is in the Classic 3D mode. Not all shots can be successfully camera tracked. This one looks like it would work fairly well without removing the lens distortion and would probably work very well if you could correct the distortion.

Moved to AE forum.