Railroad track is an interesting engineering problem. There needs to be some "slack" or freedom to move in the components. Some examples of what happens when track is too rigid. Track laid into the Powder River, Wyoming coal fields was concrete ties on limestone ballast. As the rails flexed under the weight of loaded trains, the ties rose and fell on the limestone, pulverizing it. The "fines" washed their way into the sub grade when it rained/snowed. This plugged the porosity of the soil. Pumping of the ties pulled water up resulting in mud holes that rather rapidly got worse. The attempted solution, undercut miles of track and replace the limestone with granite ballast. Now it was the bottom of the ties that were the "soft spot". A derailed wheel set dragged for miles led to the discovery the concrete ties were being abraded to the point some were less that half their design thickness. The current thought is to improve the pad design between the base of the rail and the concrete tie surface so there is some allowable flex in the rail. Canadian railroads adopted concrete ties early on as axle loadings got heavier. Most of their trees are softwoods and those ties got spike-killed fairly quickly. Rail directly on concrete abraded the concrete so that the spring clips holding the rail in place under tension lost their tension and then vibrated out of the tie plates designed to hold the clips. I've seen pictures of failed concrete ties piled up in small prairie towns.