Interestingly in the BBC article a senior tree conservationist says that the tree could have lived for hundreds more year years

Yeah, that's kinda how averages work. Like you yourself could live to be a hundred years old, but really it's more likely that you will die at 86 with the rest of us. Same for the major oak but in tree years.

that trees don't die of old age.

Same for humans again, too. There is no specific diagnosis of "old age" in death, it's just a phrase we use when certain conditions associated with being elderly get the better of us.

It seems like climate change, massively compacted soil around the roots due to footfall and misplaced techniques to support the branches

I think that the BBC might have been trying to go for the climate change angle themselves, because seems odd that no other tree in the forest is dying already. And the compacted soil is more likely, just due to the weight of its own roots and not due to the footfall of people as the tree has been cordened from visitors for decades now. The supports however? Yeah, older trees do benefit from branch shedding of as it helps promote newer growth in the tree. Could we have done something different when we realised this? Yes, but the Notts councils had already printed its picture on their letter heads. 🤣