Well, pretty much everything in this post is inaccurate. He's been a healthy scratch because TB is rotating forwards into the lineup, which for whatever reason involves Drouin. That rotation happens regardless of the player's performance. Drouin had an assist in each of his last two games, one of them pretty breath-taking, and found himself scratched last night.
He's been pretty outstanding when he's played, but is being given very little opportunity. There hasn't been much "poor performance" to speak of, and you won't find anyone who'll say otherwise. This is just what Jon Cooper does with young players, and it's frustrating to say the least.
Drouin got his opportunity with Stamkos because we had injuries. The moment we healed up, he was demoted. Since then, no LW has looked good with Stamkos, and Stamkos himself is having a sub-par season. Kucherov was in the same boat until injuries struck. Palat and Johnson, last year's calder candidates, didn't get their chance in a scoring role until Stamkos broke his leg.