The reason why the skills were combined is because they only have (non mandatory) roleplay value, and are in general only used to flesh out a character concept. The skills will never become as valuable as skills with which you have to beat a DC in order for them to work, like hide, open lock and concentration. Since bluff and diplomacy are basically covering the same area; being able to manipulate/bargain (with) others it was decided to combine the two. The combined skills now represent your ability to influence others, so the skill is appropriate in both situations. Same goes for taunt and intimidate, the skills even more so cover the same area, the only difference is that one is used in combat and the other outside of combat.
I don't really see what the benefit would be of splitting them up again.
OT: This topic has been discussed numerous times already.
The skill being used to sketch how fearsome and wicked your are or to simply frighten others by displaying your power is a fine use of the skill, and bonuses because you look frightening would be fitting. In PnP one would get size bonuses because you come of more imposing on smaller targets, but since intimidate is not an opposed roll in PotM, those bonuses cannot be added. Even though this is the use of the skill you see most, it is often forgotten this is not the "main" use of the skill, it's just an additional way the skill can be used in, and has minor effects.
I see the use of the skill intimidate in (close to) combat situations as a way to make you look stronger than you actually are. I.e. an average looking guy coming across as some one who could beat you up easily, while in reality you are evenly matched. Making some one believe you are going to use force if he doesn't listen, while in reality you are trying to avoid it. Making some one believe you can hit him where it hurts him the most (family/reputation/money), while in reality you can't or simply don't want to. In the end, this type of intimidating is basically aggressive bluffing. You can look as frightening as you want, if you don't get your message across it's not going to add anything. This is also the type of intimidation with more major results.
To put it into perspective a bit, the results of the two types of intimidation according to PnP:
- The result of the one I described first:
If you win, the target becomes shaken for 1 round. A shaken character takes a –2 penalty on attack rolls, ability checks, and saving throws.
This basically means people think you are scary. It doesn't really do anything besides that.
- The results of the one I described second:
If you beat your target’s check result, you may treat the target as friendly, but only for the purpose of actions taken while it remains intimidated.
This means you can get someone to do things he'd normally not do, i.e. back off or say something he'd usually not.
I suppose you can see for yourself that the effects of the latter use, the charisma based version, are a lot more impacting than the use I described first. Obviously the latter version is the main use of the skill and the reason why it's charisma based.
In my personal opinion the skill isn't perfect either, but it covers such a broad area that it cannot be perfectly logical in every situation. Too bad the use we're seeing most is the illogical one. We'll just have to live with it. Don't forget there are no official rulings on how to react to intimidation, this means you can't demand a certain reaction of someone.