Because there's going to be reduced import levels, meaning clubs are going to have to find Brits from somewhere. Say 10 imports each, meaning for 6 clubs that's over 20 new Brits. There might be some Brits from Scotland/Belfast available, but they would maybe have another job outside of hockey during this season, can they afford to leave that to enter the bubble?
Plus, perhaps Duggan, Richie, Hazeldine, Tetlow, Davey Phillips etc, would be tempted to stay playing in Europe in a more official league setup, rather than this mini tournament.
No it would be a complete bubble for 12 weeks. Staying in a hotel, no contact with anyone outside the bubble, including family. That is not going to be an attractive scenario for some.