Unless you know some specifics that is not public, he would be leaving significant money on the table. That is, financially sacrificing. If a portion of salary is paid as RSU, that portion would have unvested portions carried over from prior years. My best guess would be that he is losing at least $50k until he closes the gap in about 2 to 3 years at the new job. of course the new job could pay him lot more, I am not ruling that out.

Give him credit for what he did. He is losing a lot more than us armchair pundits.