[samus]

Threads are of course appropriate to implement high-level concurrency and parallelism. But for fine-grained parallelism, they are unwieldy and have high overhead.

Spreading an algorithm across multiple threads makes it more difficult for an optimizing compiler to find opportunities for SIMD optimization.

Similarly to how modern languages make it easier to safely use threads, runtimes also make it easier to take advantage of SIMD optimizations. For example, recently a SIMD-optimized sorting algorithm was included in OpenJDK. Apart from that, SIMD is way less brittle at runtime than GPUs and other accelerators.