Questions have been asked about why most teams don't employ shooting coaches.
A good question on the surface.  A shooting coach should radically improve a team's/player's scoring percentage.  Only FT%s improve and only by 10% or less.  Not really a good ROI (Return On Investment).

Why just FTs?
This is the shot improved shooting mechanics can always help, but only by a few percentage points, which is what I've been saying for many years. Teaching the brain to shoot improves shooting all over the court and vanquishes psychological distractions.  If the mechanics of these "gurus" worked it would be reflected in all shooting percentages.  IT IS NOT.
Because a shooting specialists can shoot doesn't make them a good teacher; note the examples of Dave Hoopla, Dave Love, J.J Reddick, Kyle Korver.  Some of their students state their shot is always worse at the end of the season; that makes no sense at all.  Players should be at peak performance at season's end.

Game distractions are the culprit for poor shooting performance.  Mechanics can not fix this! 
Being "In-The-Zone" eliminates game distractions!  Knowing how to enter "the-zone" at will fixes the dilemma of game distractions!
I teach the brain to shoot and how to enter "the-zone" at will. 

Study the inadequate results of these well known shooting coaches:
Dave Hopla - Regularly knocks down 495 out of 500 shots:
Shooting Coach Toronto Raptors 2006-07 season
FT 78.8% [Not So Good],  FG 46.3% [OK],  3s 36.3% [Bad]
Shooting Coach Washington Wizards 2007-08 season
FT 75.6% [Not So Good],  FG 46.7% [OK],  3s 34.6% [Bad]
Shooting Coach New York Knicks 2012-13 season
FT 75.9% [Not So Good],  FG 44.8% [OK],  3s 37.6% [Bad]

Tommy Hulihan:
Will Cummings - Temple University 2014-15 season
FT 80.8% [Good],  FG 41.6% [Not So Good],  3s 27.8% [Bad]
James Bell - Villanova University 2013-14 season
FT 81.5% [Good],  FG 42.5% [Not So Good],  3s 37.1% [Not So Good]
Patric Young - University of Florida 2013-14 season
FT 59.6% [Bad],  FG 54.1% [Good],  3s [No 3s Taken]
Grayson Allen - Duke University 2017-18 season
FT 85% [Good],  FG 42% [Not So Good],  3s 37% [Not So Good]

Dave Guinane:
Shot Mechanics

Shooting Aids:
Completely Useless

Dave Love - A Great Shot:
Shooting Coach Phoenix Suns 2009-10 season
FT 77% [Not So Good],  FG 49.2% [Good],  3s 41.4 [OK]
Shooting Coach Tulsa 66ers 2010-11 season
FT 73% [Not So Good],  FG 47.2% [OK],  3s 34.5 [Bad]
Shooting Coach Orlando Magic 2018-19 season
FT 78.5% [Not So Good],  FG 45.3% [Not So Good],  3s 35.3% [Not So Good]

Dick Baumgartner:
Shot Mechanics Camps

Drew Hanlen:
Bradley Beal - Washington Wizards 2018-19 season
FT 79.4 [OK],  FG 47% [OK],  3s 35.2% [Not So Good]
Andrew Wiggins - Minnesota Timberwolves - Career
FT 74% [Not So Good],  FG 44% [Not So Good],  3s 33% [Bad]
Joel Embiid - Philadelphia 76ers 2018-19 season
FT 80.7 [Good],  FG 48.3 [OK],  3s 30% [Bad]
Jordan Clarkson - LA Lakers 2018-19 season
FT 82% [Good],  FG 45% [Not So Good],  3s 33.6% [Bad]
Zach LaVine - Chicago Bulls 2018-19 season
FT 85.9% [Good],  FG 45.5 [Not So Good],  3s 34.5 [Bad]

Rick Penny:
One Motion Shooting Mechanics
For a strictly mechanical system this might be the best.

Herb Magee - Inducted into the Naismith Memorial Basketball Hall of Fame:
Malik Rose - New York Knicks 2006-07 season
FT 81% [Good],  FG 39.8% [Bad],  3s 25% [Bad]
Evan Turner - Philadelphia 76ers 2012-13 season
FT 74% [Not So Good],  FG 41.9% [Not So Good],  3s 36.5% [Not So Good]
Jameer Nelson - Career
FT 81% [Good],  FG 43.6% [Not So Good],  3s 36.8% [Not So Good]

Hal Wissel  has been inducted into the Florida Southern College Athletic Hall of Fame and the Sunshine State Conference Hall of Fame:
Shooting Coach Golden State Warriors 2006-2007 season
FT 71.7% [Bad],  FG 46.3 [Not So Good],  3s 35.6% [Bad]

Bob Thate:
Shooting Coach Memphis Grizzlies 2016-17 season
FT 78.4% [Not So Good],   FG 43.5% [Not So Good],   3s 35.4% [Bad]

Chip Engelland:

Shooting Coach San Antonio Spurs
FT 82% [Good],  FG 48% [OK],  3s 41% [OK]

Team FG percentages should always be over 50% and approaching 60%.
Team FT percentages should always be over 85%.
Team 3 point percentages should always be over 50%.

70% of contested shots miss. 
The clock or attempting to draw a foul are the only reasons contested shots should be taken.

Why aren't these shooting specialists more successful? 
The high level players they're coaching have shot a million plus shots.  Attempting to change/alter/tweak/adjust their shooting form is akin to
pounding a square peg into a round hole.
Changing/altering/tweaking/adjusting a players mind is much more elegant [when one knows how].

All players have their favorite shots.
What makes these shots favorites?  They go in most of the time.  These are the only game shots players should take.
The team's goal is getting players open for their favorite shots.  If those shots are contested by a mismatch then they're really not contested are they?  This is called running an offense.
The more favorite shots players have on the court the more offensive options a team has. 
If a player is unable to shoot uncontested 3s at a 70% clip that player should not be shooting 3s in a game.
All NBA players should be able to shoot uncontested 3s at a 70% clip.  If YOUdon't - I know how to teach YOU!