A single box may have that much resources available, but no software will use them efficiently alone. You end up having issues with NUMA, with your pagetable growing significantly forcing you to deal with hugepages and eventually memory fragmentation, and who knows what other kind of lovecraftian horror coming from the sheer complexity of a single system with that much resources. Turns out scaling vertically also has cost. That's why eventually you still want to scale horizontally. And that's not overcomplicating things for the fun of it, it's just tradeoffs.