I think the previous poster was a bit off the mark though. The language performance wasn't really the issue there, rather it's the fact that they picked a language that at the time really only ran on Windows, and as a consequence they were forced into running their web servers on Windows. That choice then forces them to scale up rather than out since each instance has license costs attached to it. For most companies running on Linux, it's trivial to scale out since your only costs are the compute cost (or the hardware cost in a non-cloud model), where as it tends to be far more expensive to scale up as more powerful hardware tends more towards geometric increases rather than linear. These days the choice of C# wouldn't be such a big issue as .Net core can easily run on Linux servers, but back in the 2000s using C# was putting a pretty big albatross around your neck by way of Windows licenses.