SSDs indeed use more or less the same type of flash memory as USB sticks and SD cards, but the fundamental difference lies in how the controllers interface with that memory. While modern high-end USB memory sticks and SD cards are able to keep a sustained single write operation going at pretty high speeds, each write operation must be finalized with an update to the media's block allocation map, which is the point where the media experiences a form of throttling. Consequently this results in multiple small write operations - each of which need the same finalization procedure - bringing the performance of the stick/card to a complete crawl, with even read operations being blocked.