They would have seen our ZTEM data and know (as we do) their investment return would be vastly greater. And with the profit they make with us, can then buy the copper/moly coming out of the more advanced/producing NAK pebble!
I think they left NAK because they know something about the timing to get out, just like they knew about the timing to get in, simple. Highly doubt it has anything to do with LBSR's secret mineral claims next door.