It's called "shrinkflation" where they keep the outside looking the same, especially packaging, and shrink the inside. In the case of fast food, they keep the name the same but shrink the product.

One chain that seems to be bucking the trend is In-n-Out. Their products seem to have remained consistent over the last few years except the price has gone up. They are still mobbed in Reno NV.

Fast food is still relatively fast everywhere but its by no means inexpensive, especially relative to the cost per unit. I have found Chinese joints consistently competitive in that way.