These are the two main elements of the "decline" today:
1) Exploration has been greatly reduced/eliminated, both via smaller maps and via quest compass.
2) Combat has become too easy. It doesn't require much preparation and there aren't serious consequences for failure.
I'm not sure we can say these things "crept in quietly". They came pretty much at once, usually around the time of the launch of each successive console generation.
Bullshit. Those aren't the "two main elements of the decline". I challenge you to name just one decline-saturated game that would become a good game instead if those two elements were ameliorated.
Certainly where cRPGs are concerned, the symptoms of the decline comprise a systemic rainbow of which the elements you name are only a couple of cogs. Every facet of each game is affected: The way dialog is written and structured, the way it's presented to the player, how the player chooses responses during dialog (a static, non-CYOA list to exhaust in BioWare games, for example), characterization, the combat difficulty and how it's approached (as you say), the way combat is designed regardless of how difficult it may be, consequences for failure (as you say), choice and consequence of lack thereof in the overall gameplay, world reactivity/interactivity, the potential for exploration (as you say), the way the game mechanics work, the way the UI is designed, how the control scheme is designed, whether the developers choose 3D and real-time because everything has to be 3D and real-time, inventory management... and yes, innumerable simplifications (reduced and simplified stats/skills in each new Elder Scrolls iteration), "accessibility" concessions (instant travel), overall dumbing-down, and "convenience" features.
There are tons. All of those are just what I can think up in the space of a minute as I'm writing a paragraph.