It's a myth that the league as a whole is trending away from 7 footers...it only feels that way because the Warriors, Cavs, and Rockets have had success playing small ball, and that success is much more due to overwhelming talent than to any kind of tactical advantage gained by going small.
It's not necessarily that the league is trending away from 7-footers. It's that the league is trending away from slow-footed 7-footers that can't stretch the floor. You can go through every team's lineup and see the trend.
Brooklyn - athletic shot blocker
Boston - they've got Baynes out there taking 3s
Philly - Embiid takes threes + he's a freak
Toronto - Valanciunas now takes 3s, but pushed to bench
New York - KP
Milwaukee - Brook takes threes now
Indy - Turner takes 3s
Detroit - athletic shot blocker
Chicago - I don't know what they're doing here
Charlotte - one year of Dwight was enough
Orlando - Bamba and Vuc both stretch the floor
Atlanta- I guess Len?
Miami - Whiteside holding it down... for now
Washington - another Dwight experiment
Utah - athletic shot blocker
Denver - Jokic is a freak + a shooter
OKC - athletic shot blocker
Portland - they've got Nurkic shooting 3s
Minnesota- KAT
LAC - looks like Gortat
GS - Boogie, if healthy, is a freak + shooter
Sacramento - no clue
Phoenix - Ayton will probably stretch before too long
LAL - JaVale (lol) but experimenting with super small ball
Houston - athletic shot blocker
Dallas - athletic shot blocker
San Antonio - no clue
Memphis - Marc shoots
NOP - AD
Basically, if you're a plodder, you have to shoot threes to survive.