SSD's write at the page level. If you are flipping bits in a page it has to read the page, update the bits you asked it to update and then write that page somewhere else (for wear leveling purposes).

Thus the cost to do a write that doesn't completely replace the page is a per page cost, not a per byte cost. Thus if you have very small writes you are going to get terrible performance. By extension this also leads to write amplification from a wear perspective.