I think it's important to realize a few things with Terraria as a whole, and I'll preface what I'm about to say with that I'm no game development expert.
The game runs on Microsoft XNA. Re-logic has many talented developers, but writing on a code base that had it's support dropped 11 years ago or so likely isn't a fun or quick process. There aren't tools to help develop anything new, so everything has to be made from scratch.
There is a massive amount of nuance in the game ranging from mechanics to items and how they interact with each other. You may not think it now but imagine getting an update you've been waiting for for years and it turns out to be buggy and has missing features, so you end up being disappointed and drop it with no interest. That's how I felt about the 1.2 update on Xbox years ago, and I'm sure Re-logic would like to avoid that and deliver the best product they can.
The update is coming.