There are, unfortunately, 3 different reasons that is an issue.
1: Sony and Microsoft issue the testers assigned to the game. That means 505 and Engine are not allowed to pick people to test the game for them, as they are assigned people who test multiple games on a daily basis as their jobs.
2: Long periods of testing are non-economical for 505. Terraria is not the only game that they publish, and due to that, do not use all of their alloted resources into just this game.
3. Andrew has a very different type of coding style than Rudi and his team, let alone, Engine codes in 4 different languages, including other games entirely. Like I said, they have limited resources, and due to that, would still be buggy regardless.