I suspect that ageism in tech also contributes to higher levels of risk taking - if we know or believe we will be put out to pasture at 40, it makes it more urgent to get a big payout at some point along the way.
I look at it this way. Everyone's career is a baseball game. Most workers get 5 or 6 at-bats throughout their lives, and can afford to just go for base hits. A tech worker gets 1 or 2 at-bats so he has to swing for the home run if he wants to score.
Notice that many of the arguments presented here about why younger workers are favored would equally apply in more conservative professional fields, like law - it's certainly not the 50y old partners doing all-nighters on a regular basis. But there does seem to be a certain level of inter-generational respect among lawyers that is absent in tech. Why, I don't know.