Picking up key items is irrelevant, as you progress through those games without being able to a) miss the items and b) go back to get items you might have missed. Compare an older Resident Evil (Code Veronica) with RE5 or RE6. The old game showed you many rooms and left you to decide, in which order things had to be done, before progressing to the next area. The new games usually have a room full of enemies and a cut scene, followed by another room of enemies and a cut scene.

Since the common sense is now to think, that backtracking is a no-go, the entire Action-Adventure genre has turned into a very linear Action genre. I always enjoyed linear shooters, but I want something with more depth from time to time. However, I don’t always have the time (or will) to play a quest-driven open-world game, because the majority of open-world games is largely repetitive in terms of game play and design.

This is, what people try to say, when they oppose linearity. Most people just lack patience or even writing skills to express, what they really mean. I also don’t think that most gamers really care. As sales numbers might tell, the modern linear games sell to a broader audience, than the classic complex games. It’s just sad, that an entire class of great games had to extinct.