There are many different possible reasons for the popup.

Some people get the pop simply because they haven't been doing spending on each of their cards since getting the signup bonus.

More about that and other reasons in this giant thread:

https://www.flyertalk.com/forum/amer...ne-2018-a.html

And there's other things can make Amex not want give you bonuses:

Amex USA terms now penalize:abuse,misuse,gaming;1st yr downgrade/close;leaked offers.