I don't mean to be harsh, but this is the only way I can describe it: I think it's because they actually don't have well thought out reasons for lots of the things they do, and they don't want that exposed because it could weaken their already shaky worldview because then they'd be standing on shifting sand, not a stable bedrock of unquestioned ideas.

So they just continue accumulating possessions like the happy people in the movies do, ignoring the mounting evidence that these things haven't made them happy in the past, but just one more possession, maybe that'll be the one before I happily drive off into the sunset with the end credits rolling.

Maybe I'm rambling, but I struggle to understand why some people keep doing the same things and expecting a different outcome, and asking them "why?" rarely seems to elicit a well thought out answer. The answer in the end just seems to come down to, "because that's what I do".

Some people are not introspective. As an introspective person myself, I always attempt to understand why I do what I do, admittedly that can be draining at times and doesn't always come up with meaningful answers, but I'd personally prefer to at least attempt than to wander around in wilful ignorance.