There are plenty, but here are the three that are in the front of my mind right now, besides all the dead people and all the dead species from our (and I mean me too) idiocy and self-indulgence these last two and a half decades…
a) we have a bunch of burnt-out/cynical activists (who serve as a warning “do not enter”)
b) the issue has become “background noise” – just another issue among dozens (hundreds) of unresolved/semi-resolved/unresovable issue
and therefore a sense that it is self-harming to even try.
c) Sensible/”gentle” options are no longer on the table.
That said, we WILL do things. Expensive, brutal and futile things. We will militarise our borders (more). We will geo-engineer as a last throw of the dice (sulphur cannons, iron filings, genetically modified organisms as bio-CCS etc etc). The species won’t, probably, go down without a fight. A fight mostly against its own cupidity and stupidity, but there you have it. As Bart Simpson used to say “me, what are ya gonna do?”