There is no reason trim needs to be done in the OS. (Not that I know of any drive that does this, but it should be possible without any OS interaction.)
Prior to TRIM an SSD had to assume that any block that had ever been written was still in use by the filesystem. If you end up creating lots of temp files, for example, the SSD will think that you are operating at capacity saturation regardless of actual usage. This can result in uneven wear leveling and excessive physical fragmentation which could decrease performance and useful lifetime of the drive. Additionally, it could increase the need for "write amplification" which also negatively impacts performance.
Without TRIM, there's no way for an SSD to know (without cheating) which blocks are considered free by the filesystem. Increasing the FTL free space allows an SSD to absorb more writes at full speed before needing to GC.
A SSD that understands NTFS and the other major file systems while "cheating" is not impossible. Also The TRIM command does not work on RAID volumes so there is plenty of room for improvement.
Sometimes you need to read more than just the first line to know what's going on.
"More recent SSDs will often contain internal idle/background garbage collection mechanisms that work independently of TRIM; although this successfully maintains their performance even under operating systems that do not (yet) support TRIM, it has the drawback of increased write amplification and associated increased wear of the flash cells.[4]"
