As you work in tech for a number of years you discover that (a) employers don't become permanently more loyal or generous to you if you "work your ass off" and

As you work in tech for a number of years you discover that (a) employers don't become permanently more loyal or generous to you if you "work your ass off" and (b) working long hours doesn't actually make you more productive overall anyway. I suspect one reason for ageism in the industry is that management are too inexperienced themselves to have discovered either of these.