Because I don't believe that market crashes necessarily hurt or benefit anyone any more or any less than market booms.
Booms and crashes are part of the same cycle; one MUST follow the other; and neither can exist without the other. They are like yin and yang.
And in case you do not believe me when I say that people can benefit from crashes, well, you can read
this post of mine. And also this
post.
And yes, market booms can hurt as well as help people too. Simple example: when times are good, more people choose to eat at expensive, high-end restaurants - therefore cheap dining places suffer. When times are good, people buy more brand new stuff; therefore secondhand retailers suffer. Etc etc.
Where you want to be, as an individual, is in the right place and time for a crash, if a crash is coming; and the right time and place for a boom, if a boom is coming.