There is a big difference between decoding covert and even "imagined speech" and decoding "thoughts". In covert/imagined speech decoding, the user actually trie

There is a big difference between decoding covert and even "imagined speech" and decoding "thoughts". In covert/imagined speech decoding, the user actually tries very hard to imagine the action of speaking and moving the corresponding vocal articulators, without actually doing it. This is similar to mental motor rehearsal done in sports training. It works because there is direct correlation between the speech-motor cortex and how the vocal articulators (larynx, tongue, etc) move, and how that combine to produce speech. Abstract "thoughts", on the other hand, are not so straight-forward. For one, there's no central location in the cortex where the concept of "car", for example, lives. The distributed representation of abstract thoughts within the brain makes it orders of magnitude more difficult than decoding speech for one specific individual. Then add orders of magnitude of orders of magnitude to generalize that to different people.