A lot of modern notebooks have no back access panel. Why?

@uzugiulio as you can imagine this will all only be speculation. Only the manufacturers will know the answer for sure. I could imagine that this is partially done so that people like you and I cannot service our hardware. Anytime something breaks you will have to go to an authorized service center. So it'll keep the end user away from doing repairs. Secondly, due to change in architecture i.e. soldered RAM (not replaceable) and SSD card instead of hard drives will ultimately require more of a teardown than a simple hatch to replace parts. For as long as consumers demand faster, smaller and more efficient hardware, this trend will most likely continue.