We do often write off an entire server because a single component fails because the lifetime of the shortest-lifetime components is usually long enough that even on-earth with easy access it's often not worth the cost to try to repair. In an easy-to-access data centre, the component most likely to get replaced would be hot-swappable drives or power supplies, but it's been about 2 decades since the last time I worked anywhere where anyone bothered to check for failed RAM or failed CPUs to salvage a server. And lot of servers don't have network devices you can replace without soldering, and haven't for a long time outside of really high end networking.

And at sufficient scale, once you plan for that it means you can massively simplify the servers. The amount of waste a sever case suitable for hot-swapping drives adds if you're not actually going to use the capability is massive.