X-risks are a tragedies of the commons
Safety from Xrisk is a common good: We all benefit by making it less likely that we will all die.
In general, people are somewhat selfish, and value their own personal safety over that of another (uniform) randomly chosen person.
Thus individuals are not automatically properly incentivized to safeguard the common good of safety from Xrisk.
I hope you all knew that already ;)