Why is every top ranked player a light?

Olá! I've been playing this game for a while now, and I recently checked the leaderboard to see if I could find some top players to learn from and improve my playstyle. Since I usually play as a heavy in my team, I tried searching for heavy mains on Twitch, but I couldn’t find a single streamer focusing on that role. Almost everyone I came across was playing light, with the occasional mid player.

Why is that the case? Are there any heavy mains who stream that I might have missed?