Because Self and the players have publicly stated this was Manning's #1 duty. Morris' brother was the 14th pick in the draft. Danny even got Cole Aldrich into the lottery.
Why it's not conclusive is that if it was your entire hypothesis would fall apart.
EDIT:
I doubt this will have any impact:
http://www.espn.com/mens-college-ba...2-ku-assistant-danny-manning-ready-head-coach
More bigs Danny helped at KU:
"Otherwise, Manning has helped every other KU post player with the above-mentioned figures blossom into a professional-caliber player. The list of NBA draftees includes Wayne Simien, Julian Wright, Darnell Jackson, Sasha Kaun, Darrell Arthur, Cole Aldrich, and Marcus and Markieff Morris. Others such as Padgett, Jeff Graves and C.J. Giles have earned money overseas."
""I'm blessed to have even met him," said Markieff Morris, who is in his first year with the Phoenix Suns. "He's the best big-man coach in the country. Any time that whistle blows and you look over to that sideline, he's telling you what to do.
"I owe most of my success to him."
"Danny is the best when it comes to teaching guys about footwork and angles and putting yourself in a position to make something happen." (hmm take a look at JC's footwork)
"That obviously played a negative role in his playing career," Self said, "but it was probably a positive in his coaching career. He's had to teach guys to do it the way he had to learn to do it after he was hurt, as opposed to just being a superstar. A lot of guys can't do what superstars do."
I'm heading out for a while, but you can't get any better than looking at how many bigs became successful. How they think of him. How his boss thinks of him.