One potential reason: now that CPU clock speed is plateauing, parallelism is the main way to juice performance. Many apps try to take advantage of it by running N processes for N cores. For instance, my 22-core machine will use all 22 cores in parallel by default for builds with modern build systems. That's compiling ~22 files at once, using ~5x as much RAM as the 4-core machines of 15 years ago, all else being equal. As parallelism increases further, expect your builds to use even more memory.