Explanation on why Tim Lincecum was the best pitcher in baseball 5 years ago and now considered one of the worse?

Lincecum was a 2 time Cy Young winner, led the league in strikeouts 3 times, had his ERA below 2.75 three times and was once considered the ace of the Giants pitching staff.

The past 2 years, he's loss 29 games and this season, his ERA is 9.90!

What gives? What happen to him and will be make come back?

https://www.youtube.com/watch?v=MdZ_9DJD3EM
Leonard asks
my answer:
It's scar tissue in his rotator cuff group that's caused a reduction in his velocity, and that can happen to any pitcher...especially pitchers with mechanics issues.