OVA's are less demanding on the production crew since they don't have a weekly dead line to meet along with the fact that they get a buttload more time to deliver just a single episode. With a TV airing, they get less time but need to produce more episodes, something GoHands probably aren't able to handle, since they have the K anime to worry about which will be airing really soon.
This way they're able to stretch the life-span of the series out over a longer period of time, whilst also encouraging manga sales give their pattern of releasing the OVA's with selected manga volumes.
It's nice to see that they're still supporting the series by making more animated content for it. It shows that they still care for the franchise and want to keep interest afloat for it
