No one is forcing these companies to offer these salaries and perks. They’ve decided it’s worth it so they can have their pick of employees. Having worked as an employee and a vendor at several of these massive tech companies as well as consulting for many smaller companies, there’s a few things I can tell you.

1. The caliber of employee tends to be extremely high at the big tech companies. Will you find some low performers, of course, but typically speaking, the average employee is highly educated, intelligent, and ambitious. Indeed, the biggest reason people leave these companies is because they want more control over the decision making and the ability to move faster than a big company can move.
2. The HR department knows exactly what they are doing. They’ve measured the impact of each perk and its impact on morale and employee turnover. Furthermore, every position’s salary range has been thoroughly researched and approved by multiple teams (HR, Finance, and the hiring org)
3. Losing a top employee is devastating. Not only is the hiring process extremely expensive, the loss of in-house knowledge can completely (and routinely) destroy a project or initiative. When your software generates hundreds of millions of dollars each year, keeping those top performers is absolutely worth millions in perks, bonuses and raises.

I know it sounds crazy, but these companies are full of people that actually know far more about the impact of their hiring practices than you do.