I've always wondered why the Thieves Guild is the only guild without followers.

I mean all the other factions have followers, except the TG. I would've expected that followers would be available given the fact that Vex and Vipir did a mission together as Vipir says when you talk to him.

What do you guys think?

I always wanted thieve guild follower would have been nice to have just one glad I have pc to change that.

They're thieves, they aren't meant to fight.

I think it would've made breaking into people's houses, pickpocketing and other thieves related things more interesting.

ahhh but they could place poision

Yes it's easier to remain undetected by yourself.

Slip in and slip out know ones the wiser.

Yes thieves don't want followers at all! A bad plan.
Actually followers (in general) are bad news. They will svck up all your experience like a black hole...
Unless you're the Lonely type who craves companionship (and will gladly give the skill development away).