AT&T Stadium in Arlington, Texas has been on the list but because of the said reason above, FIFA has decided that it will be more compelling to the people around the world if they will hold it in the home of New York Jets and New York Giants. Also, MetLife has been chosen to host the final game because it can cater more audience.
In terms of capacity, there is not much difference between the AT&T stadium and the MetLife Stadium. IMO, the fact that weather at that time in Texas can be extremely hostile probably turned the tables for the MetLife stadium. And I haven't heard anything about the capacity in these stadiums getting increased. But there is plenty of time, as the next world cup is three years away. The Lusail stadium, which hosted the final between Argentina and France in the FIFA World Cup in 2022 also had a similar capacity (88,966).
In fact:
I guess an extension factor to increase the capacity of this stadium is also included on the stated amount of expansion aside from making it a soccer format to match the FIFA requirements.
Also, I don't think that an argument is needed for this because the FIFA has already said that MetLife will the one that will be used in the final game of the 2026 FIFA World Cup and not the AT&T Stadium. We can also say that there have been discussions held at first before they decided what stadium will be used because it's not that easy to choose what stadium is eligible.