[DoodleDawg]

Tebow spent two years working with Brady’s throwing coach to work on his weak throwing.

Why didn't he work on it over the 15 or so years prior?

[Ingtar]

Until he hit the NFL, everyone told him how wonderful he was - sort of like NBA players currently. No one corrects issues for fear of chasing a prospect away.

[jwalsh07]

For the same reason Julius Irving did not develop a jump shot until his 3rd year in pro basketball. He did not need to to win games.