Teams are figuring out that rather than use a TE to block a guy in the box, you can use a WR split out to pull that defender out of the box. In a league where teams pass 60% of the time, a 3 WR package is always going to be a credible threat.
The Rams are really interesting in that they run 95% of their plays out of 3 wide. Not 4 wide, not 5 wide, they literally run 11 personnel on virtually every play. This both keeps Gurley in favorable situations running against nickel fronts (are you really going to go to base defense against the Rams?) and disguises their intentions on every snap. Kyle Shanahan likes to do the same thing - he's one of the few guys left who still like FBs and 2 tight end sets, but he's literally run entire drives out of one repetitive formation to avoid tipping his hand.
That's one of the biggest problems with Dallas IMO is that we telegraph our intentions way too easily. If there's two tight ends on the field, pack up the box, the Cowboys are running. If a WR's motioning inside, pack up the box and keep an eye out for the sweep. When we're running for power, we tend to look like we're running for power and we make it way too easy on the defense.