I feel overconfidence or complacency comes into play. Even older/more experienced riders get complacent or over confident.
Folks generally feel safe in known environments. But ride someplace you have never been and the feeling of not knowing what's around the curve replaces the feeling we of familiarity we have at home from riding the same road hundreds of times.
It is truly a dangerous mode of transportation. No protection even with the best gear. Arms and legs get broken and ripped off when ejected from the bike.
And yet we all still continue to ride. Those that ride will continue to ride. The ones who crash either get up and go again or not. Same applies when we learn to walk as toddlers so there is no winning, just trying to minimize risk.
Now who wants to race me down the hall with these scissors?