5E still has that new game shine. People are still excited about it. Every new release is an event and something to be talked about. People seem to be eager for new material (races, spells, monsters, adventures, etc).
Part of the reason for this is that there really isn't a lot of material out there right now. Official WotC products are few considering the game has been out for 7 months. 3rd party products are also scare as everyone waits to see what type of OGL is released. Scarcity is heightening the desire for more product. This has helped sustain the initial infatuation/love with 5E. (After all, they can't mess up what they already have if they don't release anything new.)
However, at some point this scarcity will come back to bite them. People will begin to lose interest as there is nothing to get excited about. Take a look at Pathfinder and their Adventure Paths, which is their primary business model. Their Adventure Paths come out once a month and a new one starts every 6 months. People can get excited about a specific Adventure Path and just as that it starts to wane, a new one comes along to get excited about. Along the way, people keep buying at least one product a month (more if they like all the accessories for that Path).
WotC needs to keep people excited about 5E. Right now it is still strong, but for how much longer?