Regardless of what the original constitution said on roads only going to post offices in the early days, I don't think the founding fathers had tractor trailers loaded with goods to deliver or cars that could drive vast distances across the country in mind when they wrote it. Times change. Technology changes. And I don't even think the founding fathers thought the constitution stipulations were so timeless that they would always be relevant without need for amending. Some things like rights are timeless. But other things like infrastructure are not. But all of this is beside the point. I'm not for all government being run by the federal level, but I still recognize it has it's place in some situations.
The 20th century came. The founding fathers had no idea the kind of shoes the world would rely on America to fill. Jews being massacred, entire nations like France and Britain poised to be ruled from Germany. I don't believe the Allies could have singled highhandedly conquered their foes on their enemies own home turfs without America behind them with the biggest war machine in history. That could not have been made possible by dozens of separate states all fighting their own war their own way individually. It was only when ALL of the States of America pooled their combined resources, came together as one and coordinated as a single unstoppable unit that America was able to stand with the kind of needle like focus necessary to stop one or the worst tyrannies the world had ever known and play a crucial role in liberating an entire continent.
The founding fathers never could have imagined us ever doing any of these things. In another life, maybe America just always stayed in it's little corner of the world with every state going in their own separate directions under a banner of neutrality when the powerless were pulverized by a fanatic or over grown bully. But whether they would have liked it or not, America became a world force in a way they never imagined and we had to adapt accordingly. That sometimes means having a Federal government, to offer a single, coordinated voice for some things, not all, that we all invest a portion of our pay checks into. Some things no one state can accomplish alone.