the nostalgia is there, its just that the average 10 year old kid in the UK no longer wants the type of game Nintendo produce, they would rather have a tablet/phone/shoes these days.
Most of the UK Nintendo fans are in their mid to late 20s or older at this point, the kids that grew up on DS mania are now older teens and don't want to play "kiddies games", as the social stigma around doing so isnt cool.
After all if all your friends at school are playing call of duty and GTA V, you cant really join in with "ive been playing captain toad" as an icebreaker.
Nintendo focus on, and cater for, a very specific market, pretty much a niche market if you will, and with each generation the popularity and proliferation of that "type" of gamer shifts, taking Nintendo's sales along with it.
