It's not solely Nike's decision. Amex has brand guidelines.
However, as I've said before, if the club had shown shirts to a focus group at the early stages, and everyone complained about the cheap Amex logo (which, let's face it, isn't good for American Express), I'm sure the club could have...
You can say it as many times as you like.
You can't buy an Albion home shirt, without the logo and sponsor, off the shelf.
It's a bespoke design/colour combination. End of.
I replied before. Same answer: no, it's a bespoke kit, created for the Albion.
You can buy plain versions of the 2nd and 3rd, without badges, from numerous online stores. Links in other kit threads.