The plan is for Roman Reigns to be "the guy" but you can't just shove the title on him and go, there you are. They have to build him. Lesnar will win the title on Sunday and hold it til next Wrestlemania, Roman Reigns will have a couple of feuds to build his character (starting with Orton),win the Rumble and beat Lesnar at Mania. Then he's there.
Also, Lesnar has done some pretty decent stuff and is a believable monster heel at a time when decent heels are severely lacking.
Aside from that, The Usos have had the titles for an age, and are getting great PPV booking at the moment, so they're going with them as well. The Wyatts too have just come off a big feud with Cena (who whatever anyone says is still the man at the moment) and now are going with Jericho, so they can't really be accused of not pushing them either.
There's still tons of talented guys there though, Cesaro/Rusev/Ziggler/Barrett to name a few (and AJ/Paige are dragging the women's division back up). If you liked the actual wrestling rather than the crazy storylines of the Attitude Era there's still plenty to be had now.