Answer to Question 1
To make such a long, narrow part by injection molding the mold must be quite large and the flow to fill the mold would be difficult. Blow molding, on the other hand, would be ideally suited technically because the parison would be long already and forming to the shape indicated would be fairly simple. Thermoforming, too, would be technically simple except for the possible problem of uneven sides where such a deep draw relative to the diameter is required
Answer to Question 2
The thinning process is a movement of material due to stretching. When the movement stops so does the stretching. Expansion of the material into a mold may attempt to draw material that is touching a solid object, but the resistance to movement of that material is much higher than the resistance of free material, so the free material moves and therefore stretches.
