WotC views FR and DL as the two great IP creation successes. I'm astonished they ever let DL go in the first place and am not surprised they want to bring it back in-house.
If anything, it might be a result of the sales of Eberron. The Setting Search that produced Eberron was an attempt by WotC to engineer the kind of success they had with FR and DL, and never had with Dark Sun, Planescape, Birthright, et al.
If Eberron underperformed, it would be natural for them to say "let's get DL back in house." It's one of their huge hits.