>>9902743gamers in general are too busy playing the game to give a shit about merch. Kiddie shit makes money though, because kids still like toys.
You only see demand for toys years later, which drives up the resale value of shit you bought on clearance.
So it's not just Blizzard, as stuff like Assassin's Creed, Crysis, Destiny, Tomb Raider, Fallout, Fortnite (6"), Cuphead, Kingdom Hearts, Mortal Kombat, Ratchet and Clank, Killzone, Mass Effect, and who knows how many more toylines based on video games skewing for older demographcs have bombed in stores.
There's a few exceptions, like Call of Duty, Halo, and Fortnite (the cheaper 1:18 line), with the latter being popular with little kids, and hteir success likely lies in just being generic military shit. Army men are everygreen toys and having a noticeable brand likely allowed them to sell more. Halo is also a long standing franchise, but it's also bombed and fallen out of favor more than a few times.