If someone offers a blue chip prospect (top 20 in the majors, after that success rates plummet) it's a no brainer.
But if Hernandez has 4 WAR potential, why trade him for a guy in the minors with 4 WAR potential and a much lower floor (since Hernandez is already an average, i.e., 2 WAR ML starter).
Same with Galvis, at worst he's a premier utility guy who can play all 3 IF spots, you don't trade him for say a pitcher with #4/#5 potential - that we have plenty of.
There's simply no reason to rush into any deals, if these players aren't worth a blue chip prospect, there just isn't much downside to waiting, at worst we get a 3rd tier instead of a 2nd tier prospect, but we have so much depth that's a small opportunity cost for both strengthing the ML team today and hoping for more upside in the future.
If a trade is made, I see a July move, packaging Galvis and a veteran starter to a playoff contender that needs to patch some holes and has a top prospect blocked by a player already on the ML roster. It also broadens the teams that might trade, we can eat some of Hellickson's/Buchholtz's deal, and give them a low cost starting SS, and maybe throw in a young pitcher (Asher, VIza, etc.) for the right player. This allows mid-budget teams to justify a trade, both win now and strengthening their IF (if Galvis hits like the second half of last season he's in the top half of ML SSs).
Other next winter is when Klentak will probably get busy. Right now I just don't see anyone who'd garner a key piece, either a #1 starter, young closer or power hitting LH OF. You'd have to put a package together of undervalued (i.e. prospects who aren't that valuable right now, like Williams) players to make a deal.