What piece do you propose they get? What would you be willing to trade for it?
The Reds have harvested the majority of the cream of the crop from their farm system to acquire pieces like Mat Latos and (in hindsight, regrettably) Sean Marshall. The key pieces left have to be seen as off limits.
Do you trade Jesse Winker? The best hope for a future solution for Left Field in the absence of an acquisition? Do you trade Robert Stephenson and your best shot at filling the gaps when 1, 2, or even 3 of your current stellar rotation move on after becoming too expensive?
Walt has pulled very few moves of the variety the Grumpy Fan is seeking, and I would be shocked if he puts one together in the coming weeks. The fact of the matter is that any potential moves need to be approved (and more importantly, paid for) by Reds owner Bob Castellini. The Reds are said to be at their ceiling regarding payroll, so any deal that would bring a premium player that would be more than a re-tread would require the Reds either ponying up cash or parting with even more of the sparse talent they are holding in the minors.
Your conclusion is right, Walt won't bring in the player(s) you think the Reds need, but it all stands to reason. The Reds have spent (and mis-spent: Ludwick, Sean Marshall, arguably Brandon Phillips, and perhaps Bailey, although the jury is still out on that one) their way into their current situation. What you see is what you're going to get, unless the Castellinis actually invent that new fruit...
Further, the team is now (at least heading into the break) firing on all cylinders, injuries be damned. I would imagine most realistic fans thought this year would be a bit of a retooling year while working through Billy Hamilton's development, the development of a 5th starter, the delayed starts of Mat Latos and Aroldis Chapman, and the resounding quietness of the offseason. Fortunately, Hamilton is playing (literally?) leaps and bounds ahead of schedule and the Reds weathered the pitching injuries well, including finding the diamond in the rough named Alfredo Simon.
Don't be so grumpy, Grumpy Fan. The Reds are resetting expectations in the face of disastrous injuries and the lack of depth or impending roster moves. I expect the team that weathered all of challenges in the first half and netted only 1.5 games out of first to do just as well or better in the second half.