“What could they possible spot on the ground that can’t be seen with their own satellites or Google Earth?”
My thoughts also.
At the time it was shot down, it was estimated to be at approx. 60,000 to 65,000 feet. At that altitude, there wouldn't be enough oxygen to sustain the engine.
Plus, if it was their intent to spy, it would have made more sense to fly directly east to the US rather than the thousands of miles NE to Alaska then back SE thru Canada into the US. The path it took appears to have been influenced by the shifting jet stream which travels west to east with shifting northerly and southerly winds.