But... I don't get it?
Why put a char on a shelf. There is a gazillion things to do. Lots of Operations, tons of hard modes, tons of PvP, a gazillion dailys. I don't get it?!?
I want to get to 50 with more chars so, yes, I play alts too, but why shelf a char at 50? It's then the fun begins!
Not everyone enjoys repeating the same instances/dailies/ops day in, day out. For those people, the only thing they can do in TOR is create a new character and play through their story.
Personally, I played WoW's endgame for WotLK. It was fun for a while, but then I realised that all we were doing was repeating the same content over and over again, and even between different bosses, the mechanics weren't different enough to make things interesting, with the sole exception of the Gunship battle in ICC. Then Cataclysm came out, and I levelled to 85 and got started with Cataclysm's endgame. Then I left WoW because I discovered it was exactly the same as WotLKs, and had no interest in doing it all again, just for some gear grind.