A Stella has all of Shimano’s most advanced spinning reel technologies. It’s constructed (generally speaking) from superior materials. It also has far more exacting tolerances and power for weight. It’s more refined, versatile, stronger, and more powerful than the average fishing reel. These differences make up the bulk of the expense, however, there is no doubt an exclusive brand premium. The Stella won't be made in anywhere near the same numbers as cheaper reels that are targeted to rank and file anglers.  Therefore there’s likely a higher markup on each unit.