Part of me thinks that this may be a sign of WotC moving on to other campaign settings as far as the tabletop RPG goes, letting the fanbase create additional Forgotten Realms stuff ad infinitum and occasionally putting out an original Realms product or a printed "best of the DM's Guild" book to keep stimulating people's interest in the setting. The novels, videogames, boardgames and so on can just keep ticking along fine - and the pace at which such things have been coming out suggests that whilst the tabletop RPG team at Wizards may be slim, the D&D brand team is very active.
The general plan as far as third party support for 5E seems to have been to be supportive of it, but only once the official WotC products have come out and had time to enjoy their "first mover" advantage. We've had about 18 months or so of new 5E Realms stuff from Wizards, capped off by a setting guide, and I imagine that you'll tend to see a similar amount of time pass between Wizards officially debuting a new setting for 5E and that setting being opened up for DM Guild contributions in future. (Assuming the Guild is even enough of a success that they bother opening it up for future settings.)
The overall model seems to be to maintain a compact tabletop RPG design team (freed to use whichever hired guns they consider to be worth collaborating with) in order to trailblaze new stuff (and we know that they've been beavering away at new rules stuff and setting conversions from the Unearthed Arcana articles), with novels and boardgames and videogames and the like emerging in the wake of that and the DM Guild providing an effective way for Wizards to service the "long tail" without having to invest a lot in it, whilst simultaneously engaging in an interesting experiment in opening up a proprietary world for fans to contribute to in a way which can only increase fans' sense of investment in the setting (with all the benefits to future products that entails).