It's "kick-the-can-down-the-road" engineering. If the server can't hold the database in RAM anymore, they buy more RAM. If the disks are too slow, they buy fast

It's "kick-the-can-down-the-road" engineering. If the server can't hold the database in RAM anymore, they buy more RAM. If the disks are too slow, they buy faster/more disks. If the one server goes down, the site is just down for an hour or two (or a day or two) while they build a new server. It works until it doesn't, and most people are fine with things eventually not working. This has only been practical within the last 6 years or so. Big servers were just too expensive. We started using cheap commodity low-resource PCs, which are cheaper to buy/scale/replace, but limits what your apps can do. Bare metal went down hard and there wasn't an API to quickly stand up a replacement. NAS/SAN was expensive. Network bandwidth was limited. The cloud has made everything cheaper and easier and faster and bigger, changing what designs are feasible. You can spin up a new instance with a 6GB database in memory in a virtual machine with network-attached storage and a gigabit pipe for like $20/month. That's crazy.