I think this one paragraph from Zach Lowe's latest column sums it up:

LOSER ON THE SURFACE ONLY: 2017 free agency

Teams spent more than expected, and as a result, the league lowered its projection for the 2017-18 cap from $107 million to $102 million, according to a memo obtained by ESPN.com. The average player salary should leap from $6 million last season to about $8 million in 2016-17, per league sources.

Teams and league officials anticipate much less league-wide cap space next summer for a much better free-agent class. Whoops.