^People always want bigger rides. If you have ridden, say, Millennium Force on a holiday, and thought it was great, then got home to hear your local park to get a Mega-Lite, I bet you won't think too good about it (especially if the park already has a huge coaster). Stealth is nothing compared to Kingda Ka, and so on. A Eurofighter is (or at least, looks) pitiful compared to other rides, say Dragon Khan or even Thorpe's own Stealth.
And UK already have Rage and Speed, so people feel that they have done Eurofighters before.
So yeah, I bet that's it. People want something new and big, not "another" Eurofighter.