It's not to motivate a particular person to deliver more, it's to ensure that you're able to hire that person - if they would pay, for example, $2million, then no one with experience at managing decent size tech companies would apply as they can get a much better offer elsewhere.
Also, CEO compensation is effectively between the shareholders and the CEO - if the CEO is making the shareholders happy and they want to gift him $200m for no good reason, well, it's their right to do so, it's their money to spend or waste as they wish, not the employee's.
The question isn't whether someone would work for $250m but would not work for $150m; the question is whether someone would or wouldn't work for you for that amount. If someone else offers $200m to the same person, they would work for you for $250m and wouldn't work for you for $150m.
Warren Buffets salery has been $100.000 for decades. And as far as I know Berkshire doesn't do stock based compensation at all, Buffet just holds the shares he always held.
To beat competitors, not have tons of beemers for beemer sake. The motivation is relative. The 3 big "robber barons" of the late 1800's use to send each other brag-grams over who was richer.
Also, CEO compensation is effectively between the shareholders and the CEO - if the CEO is making the shareholders happy and they want to gift him $200m for no good reason, well, it's their right to do so, it's their money to spend or waste as they wish, not the employee's.