If this bias exists (I'm not yet convinced it is a strong one), a very simple idea might explain it.
Nostalgia.
As one get's older, the world is certainly DIFFERENT, and at an accelerating pace.
As one gets older, generally, embracing that change, and especially that rate of change is FAR less of a universally good thing (if my experience, and my reading on the subject, is any reflection on reality).
For example, just last night while I was looking for something "different" to watch and perusing my old videos, I noticed my old VCR tapes, which I'll hate to throw out once my last VCR/DVD hybrid machine gives out, but I'll also loathe the relative cost and inconvenience of getting another VCR machine. Hell, I am now dreading the day when one can no longer get DVD's of shows/movies one wants (which is already occurring re streaming popularity for modern shows). At least DVD's can be played when I want, vs. streaming which may or may not be available for show X at time T.
Now, add seemingly most things to media viewing, and it's not hard, IMO, to understand why older people experience generally stronger and stronger nostalgia for things that have become hard to access.
Maybe it's good that everything dies. If humans lived for tens of thousands of years, it's not hard to imagine various people:
1). Sitting in their caves and railing at the modern technology of grass huts.
2). Being angry about the amount of their inflation increase on their government dole check, even while they squat in their caves.
3). Expand this to MANY examples.
Given the track record of the perma-doomer blogs, I wouldn't bet a fast crash doomer's money on their predictions.