FIFA are enforcing an existing rule. We wanted an exception but we didn't get one, as FIFA are worried that allowing one exception would undermine their ability to reject other requests from other nations later on. A responsible concern.
An interesting question is why has this suddenly become a big issue all of a sudden? We have had
international games around this time before and the England team didn't wear Poppys. Football clubs didn't typically have them on their shirt either. That is a recent trend partly driven by a press campaign to ensure everyone in the public eye is displaying the requisite level of 'respect'. It's much like the tendency for everyone who appears in front of a Television camera to have one affixed by the production staff to avoid any negative press.
This isn't about respect and remembrance. FIFA have permitted, encouraged even, a two minute silence before the game. The England team will be allowed to wear them before and after the game, the coaching staff can wear it all the time, and black armbands can be worn. The issue of if the players are wearing a Poppy symbol during the game is irrelevant. I wear a Poppy symbol on my jacket, it's not on display when I take my jacket off, that's not because I don't respect what the Poppy is meant to represent.
I suspect this is more about political posturing, an increasing trend where to be seen wearing the Poppy is more important than the cause. The use of the Poppy as a weapon for the press to manufacture outrages to either sell papers,
attack a public figure who isn't wearing one, or as a
PR tool for cynical politicians. This was never meant to be what the Poppy appeal was about.
Anyway if the FA really wish to go above and beyond the acts of remembrance already sanctioned then a more constructive gesture would be to donate the profits from the friendly to the Royal British Legion. That would be really nice.