most people at these companies don't last very long. if you doubt that, just take a look at the average person's linkedIn or resume. You'll see the average tenure at a tech company is about 2 to 3 years.
While many people do job-hopping because they might get more money etc., others value stability, short commute, a project they like, their colleagues and more money is not as enticing. Even others found a cushy job they don't want to lose - many reasons to stay.