It is clear that the people who create these concepts have never seen an iPhone disassembled. There is no way of building a slider phone without it being much thicker than the current iPhone.
This is all wishful thinking, because Apple will never go the slider design in my opinion.
I agree with you. Slider is not Apple's thing and I think they believe that slider phones break easier or something similar. Plus, it is much easier to make a nonslider thin than a slider.