Let's not kid ourselves here; Andrew Miller is the Yankees closer, even if no one will say that he has the job. At the moment, Miller has two saves, nine strikeouts, and has only allowed one hit, walked two, and hit a batter in 5.0 innings this year. Dellin Betances, on the other hand, has surrendered a run on five hits and six walks against six strikeouts in 5.1 innings. It's not a huge difference in a short sample size, but it's clear that one is having a much better season than the other and even the Yankees have acknowledged that much. At least internally, if not to the media.
Going into spring training, many expected Dellin to take over the reigns as Yankees closer, but he ended up struggling with a 5.40 ERA with six walks over 8.1 innings. It was clear that something was off with him while Miller seemed perfectly fine. There was no decision made, but there was also no way the Yankees could name Dellin the closer after what he showed them. Now, in the early goings of 2015, it looks like Joe Girardi has made up his mind, even if he hasn't told anyone about it yet.
So far Miller has pitched in three save situations to get the save on April 8, April 13 (1.2 innings) and April 17 (1.1 innings), while also getting into the 19-inning game in the 10th inning–their first inning after tying the score. Betances, meanwhile, pitched in the eighth inning on April 8, the eighth and ninth during of the 19-inning game, the seventh and eighth on April 13, the eighth in a losing effort against the Orioles on the 15th, and the seventh and eighth in Friday's game. It feels like the two have been used much differently over the first two weeks of the season, and it's not based on matchups like Girardi said it would be. Miller is very clearly being used as the closer–put him in when we have the lead, save him when there's no save situation–while Betances has been used as the setup man–pitch the seventh and eighth, try to shut down the opponent before the save situation.
It's not weird that they want to go with Miller over Betances; it makes perfect sense right now. The weird thing is that they're pretending there's still no closer when it's clear that there has been one the whole time. But why? It's possible the Yankees don't want to announce anything before it becomes necessary because staying quiet could help them in a strategic sense. By not announcing who their official closer is, opposing managers might not be saving certain players on their bench that they might normally save if they knew they were going to face a lefty/righty closer at the end of the game. That strategy can only work if they actually change things up and let Dellin close, though.
They could also be trying to protect Betances by not announcing a closer. Maybe they think that if he believes things are still up in the air, he could compete with Miller and possibly push himself to improve. Since Dellin has been struggling, announcing that he won't be the closer will only hurt his trade value at this point, so if they can do something to delay that hit, they're going to take it.
If everyone continues to pitch as they have been, expect Andrew Miller to be declared the official closer of the team (even though he already has been) sometime before May 1. When this happens, he'll join the likes of Glen Perkins, Aroldis Chapman, and Zach Britton as the rare left-handed closer. Hopefully once the Yankees stop pretending it'll all work out for the best.