It's a human reaction to not seriously consider the worst case scenario but instead pick one that is more 'do-able'.
We all do it. The difference is the scale and assumptions we make from the start.
For example, nuclear war is still a very real possibility. But who among us are even seriously considering what it'd take to ride one out?
Home invasion robberies are a growing problem, but the same applies - are we investing in the types of solid core doors, gates and fences needed to keep even battering ram gangs from smashing in on their first or second try? Most of us are armed, many have alarms, dogs, etc. but if 5 guys showed up with intent to do us ill and were armed, hard body armor and a battering ram, they'd be through our front doors in seconds and either down the hall or up the stairs yelling "police!" before we could be fully awake.
It's such a horrific prospect that most of us don't consider it.
Instead we debate bugging out or hunkering down with leisure to fortify the home or neighborhood.
Most people assume the disaster will give them fair warning.... I know I often do. Despite having much more and better "stuff" now than ever before, there have been times when it's been all over the place, or I'm on a trip and the wife wouldn't necessarily have known where to find the 'key' stuff in an emergency...
It's hard to cover all bases honestly. Sometimes I think we all need outside opinion - of someone a bit more paranoid than us perhaps.
Overpreparing (heck, we're ALL overprepared compared with most Americans) is like having too much money in the bank. It's only a problem if some other area of life and relationships are being neglected. If the family finds you accessible, your job is going well, your marriage is healthy.... I don't think being ready to drop everything and go into a "Blast from the Past" super-fallout shelter would be a crazy thing. It'd make you one in a million but not necessarily crazy. Now, losing the job, wife, and kids in order to be prepared for Armageddon IS CRAZY.