i know i might get yell at for this, but whatever:
Terraria isn't a great game to watch, why?
1. Watching someone play a game isn't always fun, Especially in Sandbox type games (unless it's gmod)
2. Terraria gets Stale after a few hours, just like minecraft, you just end up basically doing the same thing over and over, "oh wow! i'm fighting a giant brain rather than a giant worm!", yeah, thats basically the only difference...
3. Theres hardly any good mods for terraria which Add more stuff to the game, most of them just add a few weapons and Vanity,
4. Twitch has LOADS of other games people would rather Watch, e.g. TF2, DotA, LoL, BoI/Rebirth, etc.