Just to summarize.

Its obvious being that being "good" has received the bulk of the development.
With voiced characters, storylines, games, songs and etc.

Being "evil" is just a gimick to fight NPC's you would have otherwise interacted with.

Just think about it this way.
Where is the Alfira of the goblin path?
Volo? Whether I am good or not I can always get him but the only way to interact with Alfira is help the Tieflings.

I guess you could argue that I could join the Tieflings and see all these things only to betray and kill them. I mean Alfira says she is going to this famous Bard's Inn in Baldur's Gate. But if I kill her then her storyline is over...

If I was evil I wouldn't murder her for the lolz.
I would just enslave her and have her sing for me for free... seems more practical to do that imo.