No idea it might be to prevent shaming, riot also isn't able to give you information about another player's punishment or his account status, and the honor level can be related to previous punishment. ( basically if you're able to see that someone did go from honor 4 to 0 you know he got punished, which is someone you're not supposed to know. )
But really you won't get a general idea of someone until you played at least a few games together, and at least a few very bad games where the tilt probability is high. I sometimes duo with strangers, it often starts by a great game we did together and from that we might win a few other games, but from time to time one of those duo partners will get extremely toxic/mad and so on because a game isn't going in the good direction, it might not be the first bad game, but some people are really impacted by loss streaks.
Anyway, play with them, and more importantly play loosing streaks with them.