Actually there was a time when similarly looking shoot em ups and platformers were released on Amiga platform as well but compared to today's gaming world things were still better in terms of gameplay.
Maybe there were better design teams back then but these people are still (probably) alive and in the business somehow, However overall loss of quality in the industry is visible.There is one obvious reason to this, the demand is changed so did the supply.
With the increasing popularity of internet, every passing day a lot of new people (idiots mostly, there is no need to be kind or modest about this for it's a fact.) become computer users, therefore game players! This effects the demand on computer industry in general and specifically, computer games.