Because the low level details tend to change over time and then it's too late and you're committed to supporting something that doesn't make sense anymore. like

Because the low level details tend to change over time and then it's too late and you're committed to supporting something that doesn't make sense anymore. like branch delay slots in some RISC cpus, or vulkan (https://www.sebastianaaltonen.com/blog/no-graphics-api https://www.sebastianaaltonen.com/blog/no-graphics-api)