I am not sure everyone is correct about the NFL's current popularity in the UK. I have seen a number of UK articles stating the quick growth of popularity. They don't show any concrete numbers so I won't post them. This link claims the NFL is lying about it's popularity in the UK.
https://sports.vice.com/en_us/articl...its-popularity
The link does have numbers which are interesting. Even if the NFL is manipulating the numbers, I do think there is enough there to be "milked". I am against the expansion, but on the subject of popularity, I think there is a lot of current and potential future growth. International soccer is growing in the US and the Premier League is making money on it in TV ratings. The NFL could easily do that and better, and these games are only going to help that.
As has been mentioned, its not just money but ego. The ability to proclaim they are on two continents divided by an ocean. This article shows, as others have, that the NFL has big $ opportunities in Mexico, Canada, and Brazil. Them looking past these cities for London seems as much about bragging rights as anything else.
https://sports.vice.com/en_us/articl...its-popularity