For why, there's first the accessible technology: the Bath ME boatyard that built her in 1909 had a very longstanding and deep fund of expertise, equipment and materials to built what was essentially a very big wooden boat- shaping timbers, shaping planking, fastening, caulking, etc. . A steel hull required working in a completely different way: bending heavy plates, riveting them. Notice that the boatyard had tried to modernize in a couple of important ways, though: it used some iron for internal bracing, thus making the hull stiffer ( because they must have realized that hogging would be a bigger problem for such a big ship) and they equipped it with steam engines ( often called donkey engines) to operate the sail rig. This last is quite important: to get the maximum speeds, schooners ( like most sailboats) needed a lot of management of the sail rig and that had been labor intensive, even labor-destructive: men on a slippery wet deck hauling on lines to move heavy wet canvas in a high wind would often be hurt, frozen in very cold weather, and could also be lost overboard working in heavy seas out on a bowsprit. Having a donkey engine to actually do a lot of that heavy hauling was a great step forward. I have not dug deep into the specifics, but possibly the shipyard didn't quite manage to anticipate the high loading of the hull in a big storm, how much the planking would spring and allow water past the caulking. It may also have failed to anticipate the effect of the high freeboard- the more the boat sticks out of the water, the more the hull acts like a sail; and a sail that can't be furled. Having a sail that can't be furled while being near a lee shore in a very strong gale means the boat is liable to be driven onto the land, anchor or no anchor. At the least, it greatly complicates managing the boat.

The architects may have been working at the edge of their knowledge, but were not too far wrong about the economics. It seems to have been a reasonably profitable ship, making decent money from its launch in 1909 to its wreck in 1924. And they knew that the return on a sailboat hauling bulk goods might be reasonable: remember, a boat is an extremely efficient way to move heavy things: a canal boat laden with several tons of crushed stone could be powered by a single mule. The trade off is speed. As the hull is pushed faster and faster, the amount of energy required grows very quickly. A sailboat didn't require buying coal for propulsion, and if the cost of the crew was reduced by adding a donkey engine ( or two) and the cargo was not time-sensitive ( hauling gravel, say, and not people or bananas) a slower speed and longer transit time was not a great problem. Smaller sailboats would continue to operate at a modest profit well into the 20th c., when they would often be fitted with small hit-and-miss gasoline engines that gave them some useful added mobility in port and in dead calms. And compared with the modest cost and modest returns of a small sailing ship, the extremely high-cost ocean liners, burning vast amounts of coal to make rapid Atlantic crossings, seem to be the dangerously extravagant ships- and they would also become economically impossible.

I'm not sure about how the RN viewed wooden ships vs steel for strength, but of course it would have been going to shell-resistant ironclads far earlier, circa 1855, and by 1909 would have iron and steel battleships: and as speed was always of the essence, would have adopted steam propulsion earlier as well..

A delightful account of being a lowly crewman on one of the last long-distance cargo sail ships is Eric Newby's 1956 The Last Grain Race- and yes, that's Eric Newby the famous travel writer. A good account of the business of sailing a modest little cargo ship around the coast of England in the last days of sail is the memoir of WJ Slade, : Out of Appledore