Some people really love Mandos.
A lot of games don't have them at all (due to time period). Old Republic is one of those time periods where you can actually have 'em, so it'd be a shame not to.
They've got a pretty baller culture when you look into it.
I mean, just like you'd get some people going 'meh who cares about Jedi I WANNA BE SITH' you'll get some being the same about mando, but I've got a buddy who, when hearing about the game, went 'oh man I really hope there's gonna be Mandalorians I've had a concept I've wanted to play for years'