How to convey a sense of depth & distance in a landscape?

I’ve noticed that some photos of landscapes make me feel the depth and immersion, don’t know how to describe it, just the true feeling that the photo isn’t really flat.

Other photos rather look flat, even though we can tell that one object is behind another, and the shadows persist, but it just doesn’t look that “effective” for me.

So I would be happy to know if there is anything special about the photos, maybe some special technique or anything else that I haven’t yet explored. I brought few random examples from the web trying to demonstrate what I mean.

Examples of photos where I can feel the depth:

enter image description here
enter image description here
enter image description here

And here are examples that were taken with the same lens as pic #1 and #3, but don’t have the same feeling for me:

enter image description here
enter image description here
enter image description here

The fifth photo is not the landscape, and it might be not the best example at the end of the day, but the scene just has a “potential” in my opinion, but the actual photo miss the depth feeling for me.