Originally Posted by Maximuuus
I really don't understand why "origin companions" seems so popular...

Is that because we can play them as a main character ? Because that's the only thing "origins" characters are... A great background story/quest is not related to Larian's concept to me.
Players really enjoy playing a character created by someone else for another reasons than their background story ?

Can someone enlighten me about it ?

You more or less hit the nail on the head.
The origin characters are companions in the same sense as the recruitable characters/companions you'd find in any other CRPG. The difference here is just that rather than just picking them up somewhere along the road and having them as one of your party members you're able to play as one of them, thus experiencing the game and its story from their point of view. For example in their previous game, Original Sin 2, some events would play out differently depending on whether you were playing as certain characters or if they just were one of your party members. When playing as the character in question you'd usually be given multiple special options to handle various situations that'd unfold in the dialogue.