In part, it was loved to death. It turns out roots demand loose soil or at least not heavily compacted soil from the countless feet of fans walking over it, and opportunistic infection (maybe not this tree but others) is a problem with famous trees.

Propping up limbs and backfilling hollow trunk with concrete also perpetuates a surface of leaves which demands a viable root network to support it. Had they let limbs die, the trunk might have survived longer but on an "uglier" tree.

The largest Kauri pine in NZ is now fenced off. Nobody wants the risk.

"I know, lets dig a tunnel through this giant sequoia so we can drive through it" is out there.