Have you looked into what the grading process actually includes? I mean, it's not just a plastic case they're selling, it's the verification that the game is legit and the rating of its condition. Idk, maybe the prices are still too high, but for some people that sealed grade makes a big difference in resale value. It can feel like a cash grab, but there's more work involved than it seems at first.
Yeah I get that, my buddy sent in a sealed copy of Mario Kart Double Dash last year thinking it was a sure thing. When it came back with a lower grade than he expected because of some barely visible creasing he couldn't even see before, he was pretty bummed. But he turned around and sold it for way more than he could have ungraded, just because someone really wanted that sealed number. It does add a layer of trust for buyers, even if the cost feels steep for what it is. For him, the whole thing was stressful but ended up working out.