I agree, the fans need to stick together - but this does not mean that the fans should be shouted down for criticising their representatives. Organisations get better for listening too, taking on board, and evolving based on the criticism they receive.
In reference to your question, "what more could they do beyond what they tried?" I refer you to my previous post, about 2 up from your post, where I listed 7 other things they could have done.
But your list is essentially get the backing of the likes of famous footballers, politicians, even the Royal Family. That is far from easy and in some circumstance (the Royal Family), nearly impossible. It's unrealistic.
Some of the footballers you've listed, the likes of Harper and MacDonald would have as much influence to the PL as the man in the street, the others like Shearer are known to do work for the PL and might be cautious about actively backing a takeover which could have serious hiccups behind closed doors that we (and him) aren't aware of and it might be damaging for him to be putting the PL under pressure to approve it and perhaps its just easier to not do it.
Other clubs in the league don't want the takeover to go through, I think I seen somewhere yesterday that about 10 clubs actually wrote to the PL saying they didn't support the deal? Why would PL clubs write to support us when we're going to improve and push them out of European spots and extend the big 6 to a big 7? Championship clubs couldn't give a toss either, again, why would they? If they get promoted there's another huge club costing them 6 points each year, it benefits them to have another shit team in the PL.
Big businesses in the north east. I agree with you there, but again, how much influence will that have to the close minded PL executives in London? Is it worth the time and effort putting it together?
Major sponsors won't want to touch it either. Their allegiance is with the PL and certainly not us so they won't be putting them under pressure. The sponsors will still be there reaping the benefits in 12 months if we're relegated. They simply don't care.
Members of Parliament and the Government. Well apparently a lot of the Gov mps were against the deal if reports a couple of weeks ago were true, roughly around 100 of them. A lot of MPs in Parliament don't support the Saudi regime either. Again it might just be a case of it not being worth it for most of them to put their name out there and back the Saudis buying a PL club. I'm sure there is some support there and maybe there have been MPs being vocal about it.
The Royal Family. That's just not going to happen.
There's also the fact that the NUST is run by volunteers. How many people there would they have to chase up for a statement backing the takeover and how many of the successful signatures would carry any weight? How many hours would be spent chasing someone who just rejects the idea for arbitrary reasons? You're asking volunteers to put countless hours into something that for all we know will be pointless. The PL are arrogant bastards and I doubt there's anyone out there who could influence them to push this through. The amount of the investment into the league this takeover would have produced still wasn't enough so I think in the end letters and statements from whoever are meaningless.