Why is Delta Getting More MD-90s?

Delta has long had a small subfleet of MD-90s lurking around. The 16 MD-90s were supposed to be the beginning of a much larger fleet. In fact, the MD-90 was supposed to be the 727 replacement, but when McDonnell Douglas was bought by Boeing, Delta abandoned the rest of its MD-90s and instead went with the Boeing 737-800. Now it appears that Delta will be upping its fleet of MD-90s by 3, and I can't quite figure out why.

The MD-90 is actually a great plane to fly. You can think of it as a slightly stretched MD-80 with much quieter engines (actually the V2500s you'll find on many A320 family aircraft) and a more advanced cockpit. That means that for most of the plane, it is an incredibly quiet ride, and even those stuck next to the engines in back don't have an awful head-splitting experience like they do in the MD-80s. The layout is 2-3, so there are fewer middle seats on the plane. Delta has overhead screens for movies and all 16 now have wifi as well. As you can see, it's a nice ride.

From a technical perspective, it's a decent, medium-haul airplane. It has a range of about 2,400 miles in its standard form (what Delta flies), but there were also two extended range aircraft built that can give it longer legs. Delta will be acquiring one of those airplanes and two standard ones from Hello Airlines. Delta's MD-90 seats 12 up front and 138 in the back. That compares to 16/144 on the 737-800s and 16/132 on Northwest's A320s. Both those airplanes have longer range.

So what exactly is Delta getting with these three additional MD-90s? I suppose if they needed additional capacity, that would be the cheapest way to acquire a medium range airliner quickly. But Delta doesn't need additional capacity. Delta has been cutting routes all over the place, and I'm sure they still haven't rationalized all the Northwest/Delta capacity they have out there.

So I find myself scratching my head on this one. Why the heck are they doing this?