Eventually you hit a ceiling, and there aren't companies that pay better than your current employer. You're getting raises each time you switch jobs because your experience & job performance qualifies you for jobs at progressively more economically successful businesses, which both can and will pay you better. This can't last forever: eventually you get to the "center" of your industry, the set of companies with more money than everyone else, and you're better off performing better within them than finding another job.

(Or alternatively, you find a fast-growing startup that's growing faster than the wealthiest companies in your industry, hop on the ground floor for stock options, and ride the stock up. Once that happens you don't need money, though.)