Comment by daneel_w

What you're seeing are the speeds of various multi-tier caches (RAM, intermediate SLC etc.) It cannot write to its main flash memory that fast. While it to the user looks like they just wrote 10 GiB in a single second, the SSD is internally still busy for another 10 seconds persisting that data. The actual real write speed of top-shelf consumer grade SSDs these days is somewhere in the vicinity of 1.5 GiB/s. Most models top out at half of that or less.