It could be because they are gutless unimaginative trend-following sheeps.
It could also be because they just try to sell whatever it is they think most of their customers believe they want / need (wether or not said customers are right is a whole other matter)
So where is the thinner obsession coming from? Why are they removing all the ports?
Isn't it because of fashion?
Functionality and esthetics do not have to be mutually exclusive, but the people designing laptops don't seem to be aware of that.