It's not really insane. The items are super rare and people get themselves caught up in the game to the point that they're spending hundreds (maybe even thousands) of dollars to get top notch gear. For some people, this game is pretty important; for others not so much.

If you were to loot a mythic or arcane item after spending hundreds of dollars to get it, would you only sell it for anything less than 1,000,000? People want a nice return from all the money they spent in the form of AL gold.

However, like gundamsone said, the game is easily playable without opening hundreds of thousands of locked crates. You don't need the very best gear to be successful in this game.