I didn't realize loot does not respawn if a player entity has it in their possession? It doesn't seem very rewarding that nothing useful is ever present at a heli crash due to it being in the possession of a player that could, for all anyone knows, have uninstalled the game 3 weeks ago.
Side note: These high-grade loot locations should have a high risk/reward factor and if they spawned loot more often would be highly contested. The fact that players will be fighting there would reduce the likelihood of the high-grade loot being distributed throughout the player base in large quantities.