So... Look what I found on Bandai UK's site:
Bandai UK Milestones
2004
Power Rangers Ninja Storm released and continues to be the best selling boys toy. Thunderbirds toys launched to coincide with the live action movie. Other new launches include Teen Titans and Pokémon Advanced. Tamagotchi Connexion launched in May and becomes a hit again. Super Badge It! launched. Bratz wins Girls Toy of the Year. Badge It! wins Creative Toy of the Year.
2005
Power Rangers Dino Thunder launched and continues to be popular with children in the UK. New Debuts include toys on Gerry Andersons’ New Captain Scarlet, and soft toys based on Disney’ Bambi. Tamagotchi Connexion Version 2 wins Toy of the year.
2006
Power Rangers Space Patrol Delta launched and quickly becomes the best selling boys toy of the year. Other new launches include Bag It! , Unazukin, and Pocoyo a stunning pre-school property from Zinkia. Version3 of Tamagotchi Connexion is launched and continues to be the UK’s best selling toy in the UK. Total sales of Tamagotchi exceed 4 million pieces in the UK by the end of 2006.
2007
Power Rangers Mystic Force is launched and continues its excellent sales performance against strong competition from blockbuster movies. Ben 10, a new animated series from Cartoon Network is launched in spring and quickly becomes a top seller. The Omnitrix F/X scoops the Boys Toy of the Year award. Bandai return to the dolls market with Disney Fairies, a new toy line based on the ever popular Tinker Bell, and Strawberry Shortbread a heritage brand from the 1980’s. Tamagotchi Connexion Jinsei and Jinsei Plus (Version 4 & Version 4.5) are launched and continue to be the UK’s No1. selling toy for the third year running – a feat never achieved by another toy since toys record began by Consumer Tracking group NPD.
2008
Power Rangers Operation Overdrive is launched and celebrates its 15th continuous year on sales in the UK. Pokémon Diamond & Pearl toys are launched after strong sales from the latest Nintendo DS games. Tamagotchi Connexion Familitchi is launched and continues to perform well in the toy market. Ben 10 toy line extended and becomes No1. selling boys brand in March. Other new launches include Puchi Puchi – a novelty toy that simulates bubble packaging and Catcha Beast – an interactive electronic game.
2009
Power Rangers Jungle Fury is launched and continues to be popular with kids in the UK. Ben 10 moves to the next level with the launch of Ben 10 Alien Force. New launches will include some exciting girls brands including Star Friends, KeyTweens, Harumika and Tamagotchi Music Star the newest extension to the Tamagotchi brand. Celebrating its 60th Anniversary in 2009, Bandai will also be launching toys for Noddy in Toyland.
2010
Power Rangers Racing Performance Machines (RPM) is launched and becomes the 17th consecutive year of this evergreen brand boy's brand. Ben 10 fever continues to the next level with the launch of Ben 10 Ultimate Alien in autumn. Star Friends, KeyTweens, Harumika and Noddy will see new line extensions added. New launches will include Armouron, a unique new concept combining boy's action, role-play and construction. Tinga Tinga Tales; a new pre-school property to be broadcast on Cbeebies in spring and is based on the Tanzanian art style and African folklore.
So, we can see that tamagotchi was EXTREMELY popular up until around 2008, where it started dying. Imagine how much popular tamagotchi is in the USA- it doesn't look like the end is near yet. If a popular tamagotchi is released soon, then it may 'restart the franchise' and get tamagotchi popular again.