Just read the history.
https://en.wikipedia.org/wiki/FIFA
If the Home Nations left FIFA, they will think they have lost nothing, and will carry on without us. That's why they will win this poppy issue. If the Home Nations left, the sponsorship moneys will all be transferred over to the continent where it all started and will want to reside, and it will just be a FEXIT (FIFA exit) by us, and they won't care a damned thing, as Adidas is a major supplier of everything to the WC, and is a German company with a global hold. If we left, we will just be laughing stocks who they will label as countries from a by-gone era with poor footballing abilities who could not adapt to the modern game of world football, also whose leagues could not survive without inviting the world's players to drum up business and bring in more money, and they will laugh about how corrupt it is in the Home Nations that there is no restriction on said foreign players, which rule basically back-fired in stopping development of home-grown talent.
It's a loss-loss argument. We can't win. If we fight it, billions will be lost and it will become even more political and the situation will be dire.