Why are SSDs so fast compared to raw NAND?

3 is the answer. SSD controllers (and high-end USB flash drive controllers) are basically RAID controllers. This is one of the reasons that larger flash drives tend to be faster than smaller ones. Mobile devices usually don't have many flash chips and so their storage is slower.

The writing to the NAND-chips is parallelized, meaning that you are writing to say 20 chips at a time instead of just one.

This, however, is not the complete answer as the performance with the same chips differs quite a bit with different controllers.