InvalidError: I completely agree with you. However, more MP gives us more headroom for post processing.
At the expense of having noisier and less sensitive pixels than you would have by sticking with the larger cell size. You may have more pixels but they are of lesser quality than they could have been, so you may end up with worse overall picture quality.
For example, Canon's 330HS (which I own) is a 12MP point-and-click camera that was one of the best-in-class cameras of its year. The 340HS that followed (which I considered buying) is a 16MP camera but failed to get much praise from anyone who reviewed it because its pictures are noticeably noisier than the 330HS.
More MPs is not always better.
With phones and tablets, there is also the additional challenge of cramming a whole optics stack of almost pinhole lens in less than 5mm.