I think the issue people have with Norwegian is one of confidence. By which I mean that in the sphere of short haul, they were late to the party. Easy have been snaffling the best slots at prime airports for a lot longer than Norwegian and will defend their position robustly. Meanwhile on long haul, they are experimenting with a brand new (somewhat problematic) aircraft type on new routes, many of which have been tried before and failed. Likewise, long haul carriers will be defending their position, especially across the Atlantic.
Perhaps now is their time and it will be a roaring success. Perhaps it will tick over well enough to keep it viable long term. Perhaps it will end in a nasty mess next year. I think this is why nobody will leave a successful, established airline for Norwegian, no matter what the contract on offer. In short, it is an unproven business model at the present time.
Let's see what happens when Norwegian put Airbus into Gatwick and tells all the Boeing drivers based there to go and be rebased to Spain.
This is exactly why nobody who wants to be based in London would join Norwegian. If they decided it wasn't worth competing with easy at LGW then they would be the next bunch of people to be forcibly relocated onto whatever contract was on offer at the time. Just like Ryanair.