To be fair, both are CP ridden shitholes with retarded administration and dwindling numbers these days. Not hard to confuse the two
/qa/ was irony poisoned le quirky super ironic shitpost central for as long as I can remember, I don't think I personally seen it used for the purpose it was created. If it wouldn't be centered around soyjaks, it would be centered around something else just as cancerous, like touhou or my little pony(both of which were also popular on /qa/ at some point)
Touhou is centered on /jp/ and horsefuckers have /mlp/ so giving soyjaks their own unofficial board was the best thing that could have happened. Well, the administration caring what users have to say and taking actual feedback into account would have been the best choice, but for the current dead shithole with no future 4chan the best option was having a soyjak board around.