Originally Posted by sdsearch

It's not "the other bank". Both Chase and Amex banks contact Marriott about each Marriott card application. So Marriott will see both of your applications coming at once, or in close succession, and probably deny the second one, and maybe even lock you out of all later applications because you tried to "sneak around" them.

That's why "how long it's been since you got a signup bonus" is one of the criteria in some cases. It's Marriott who knows that, not either of the banks. So these criteria were designed by Marriott, not by the banks themselves. And the checking of whether you qualify is done mostly by Marriott, not by the two banks.