They are the biggest. Giant redwoods are revered for their age and size. It was not always like that.
Many of the biggest giant redwoods were killed merely for bragging rights. Whoever discovered the biggest got to arrange to get it cut down, and then pose on the stump for photographs. Some trees were cut down just so the rings could be counted. Many felled trees were just left to rot where they fell. It was not practical to transport the lumber out of the remote regions of the Sierra Nevada where the trees lived. That was at a time when ‘sportsmen’ shot from trains into herds of wild buffalo, only to pose with the biggest dead carcass they could find in the aftermath, and then leave all of the deceased to rot on the prairie.
So, at about the same time in history that the related coastal redwood was being harvested so indiscriminately for lumber, the biggest of the giant redwoods were killed primarily for sport. Even in regions from which lumber could have been transported from, no one could figure out how to get such massive giant redwoods onto the ground without fracturing the lumber within. Because their wood is so brittle, smaller giant redwoods that were harvestable were simply cut and split into shakes, grape stakes, and fence posts and rails. Young and healthy specimens of the biggest trees in the World were used for the smallest and most unglamorous forms of lumber.
The biggest of the giant redwoods are of course protected now, mostly within national parks. They are quite accessible to those who want to visit and admire them. I got this picture with one of my esteemed colleagues in front of the General Sherman tree in wintertime back in the early 2000s.