A large part is the fact that memory access is comparatively slow. Getting the data to the core is the challenge. Most processing is so fast that the operation

A large part is the fact that memory access is comparatively slow. Getting the data to the core is the challenge. Most processing is so fast that the operation you want to perform is latency-limited by IO issues. Some have suggested offloading compilation to other machines; this works, but efficiency depends on having large enough compilation jobs that this results in net benefit. Similar arguments apply to data analysis - moving the data is too expensive, so you move the code to the data instead.