Why does ssd write speed drop?

Question

Solid State Drives

Yesterday I bought a ssd Goodram CX400 1TB 2.5" SATAIII 3D TLC (SSDPR-CX400-01T) and merged data from my old ssd drive via usb3 on the disk, mostly large files and they were copied at first by 5-10GB each. After about 30GB, the speed dropped from 180 to 50MB \\ s and continued to copy at this speed. Let's say the cache is over, I thought, but after pausing copying with the Windows Explorer for 10 seconds and restarting, copying again continued at a speed of 180. And this happened several times during the entire process.
Why is it slowing down speed and why does it increase after 10 seconds?And how to fix it?
Why does the disk itself not make such pauses during the copying process?After all, this would potentially increase the speed.

Answer 1

As far as I know, SSDs need to periodically send a TRIM command so that the speed does not drop, and USB adapters do not support it.