In my opinion, Apple is making it's products thinner because of independent technology reviewers using 'weight and thickness' as one of the primary reasons for making a recommendation of a product.
I see it all the time now in review websites, technology magazines that have review sections in them, youtubers that review technology products, all of them use the the thinness of a device as a pro or con. It is very common to see a reviewer make a comment on a products thinness, then compare it to a competitors product, then decide if it is a pro or a con. You look at as many ipad/tablet reviews, macbook/laptop reviews and they all have one thing in common, which ever product is the thinnest, that is the one that is always given a 'pro' point towards it.
We the customers are the problem because we demand unrealistic targets to be achieved. A device is too small to read content on, screen is made bigger. Device is now larger which means more weight, customers complain how heavy the device now is. Weight is reduced by trimming out the thickness of the frames material. Now the device is too flimsy, it bends to easily and the moans and complaints continue.