In reference to this, I found the below in an ad:
I recently bought these drives a few weeks ago and then saw his picture. Do all SSDs suffer from such substantial performance drops over time and why?
It may seem a dramatic drop but that's not the case. Still, the chart is meaningless without knowledge of the underlying load of the drive, so mostly marketing drivel.
But yes, technically all SSDs suffer from a performance drop when faced with heavy write scenarios due to a fundamental limitation of the underlying technology itself(NAND flash).
And when you have no more free blocks, the controller is forced to perform an erase cycle(which is awfully slow compared to the other operations). This also leads to a phenomenon known as Write Amplification.
On a historical note, this used to be a bigger problem earlier when the TRIM command wasn't as ubiquitous as it is now. It was a solution to a problem arising from the abstraction of logical blocks from the physical blocks that the drive's controller performed which itself was necessitated by the need for wear-levelling.
Source: Anandtech (I've come to regard them as THE resource when it comes to SSD technology and testing). If you wish a more in-depth take on the matter read THIS. It's a little bit old, but much of it still holds.