For sure, it seems like some some RPGs/adventure games which were not originally open-world are making some sort of transition to a completely open world. Some will fail to adapt to this formula, becoming cheap imitations. MGS5 probably stands the highest chances of failure due to its tendency towards linear storytelling and heavy use of cutscenes. Although the levels in MGS are pretty rich, the overall game formula is at first glance a toughie to adapt that way.
You are probably right on some counts. Skyrim was one of the biggest successes of the past few years. There might be a pressure from executives to create more open-world games just to get a me too product out there, definitely a short-term trend in the works.
Most games are limited in some way or another, by their budget, scope, style, design philosophy, in a way that makes them unique. Sure if you had an unlimited budget, you might be able to create an AAA game which accommodates to every genre, niche, cliche, or whim. Yet the fact is that those which try tend to become ridiculously expensive, or have other shortcomings. That's the problem... a lot of games these days are trying to be catch-all theme parks which have a little bit of something for everyone, maybe holding massive temporary interest much like a blockbuster film. Pre-order this, pre-order that, milk the hype and novelty for all it's (probably not) worth.
On a more positive note, this could help to innovate gaming, creating more replay value in games which otherwise wouldn't be worth a second look after playing them once.