Why don't trains make *that* sound anymore?

Why is it so important that the stones on a real track are jagged? In the past, train tracks used to have gaps in between them. The gaps let the steel tracks expand and contract with temperature, and wheels hitting those gaps made that tuck sound. But those gaps also slowed the trains down. So, today's tracks are welded into one seamless rail. No more clicketity clack. But now, the expending hot drill has nowhere to go. And if left alone, the internal pressure would build until finally the rails would violently buckle into this zix. And that is where those jagged rocks come in. The tracks are attached to these sleepers and then embedded in those rocks. And their jaggedness makes them physically interlock, which creates a huge amount of friction. So when the steel rails expand and push on the sleepers, the jagged rocks lock together and hold everything firmly in place. That keeps the rails straight even under huge internal pressure. But if the rocks were smooth and round, then vibrations from passing trains would make them slide around and the track could quickly buckle.