Another reason is that 5e is a bit opaque about some of its design. For example, it is clear that skills are, by default, more important than tools, and some tools (thieves' tools) more important than others. The designers realize this, and create backgrounds (and other rules) accordingly, but at the same time create a feat that lets you choose tools OR skills, as if they had similar importance, which can be confusing to newbies.
I like it more now than when I first started playing (j fact, it is probably my favorite game at this moment), so I though I would share some little insights about 5e's philosophy. They might be obvious to some (specially if you're a long time 5e fan), but they may also vbe helpful if you're trying to understand the system a bit better.
The first things that comes to mind is how skills work. Or don't work, depending on what you're looking for.
The thing is, you cannot rely exclusively on skills do do things in 5e - including the things skills are supposed to do.
The proficiency bonus is small, from +2 to +6. I do like the idea of smaller numbers in general, but this means your proficiency will only make the difference between success and failure 30% of the rolls, that's on level 17. For most of your characters' career, proficiency will only be useful about 20% of the time.
This causes other unexpected effects. For example, clerics are not that good at religion, since it is Intelligence-based. Nature is also based on Intelligence, making wizards better at it than rangers and druids. Wizards do not have the option of being great at arcana; the Arcane Trickster is probably better (if that is what the player wants), since he gets Expertise, even if the Wizard casts more powerful spells.
Fortunately, the designers know this - and they have taken several steps to "fix" it, by using different features other than skills.
The rogue, being the best at skills, gets not one, but two fixes: expertise and "reliable talent" - because skills, by themselves, are unreliable.
|Copyright: Wizards of the Coast|
As you can see, if you look at the big picture, the game works as intended. But, in order to keep the "bounded accuracy" idea, it has sacrificed some degree of simplicity.
If the designers add chosen to make proficiency equal to half-level (or half-level +2, of course) for some "expert" skills, or just let advantage from multiple sources stack, or just allowed more possibilities of expertise, you could do away with multiple class features at once - making the game a lot simpler.
On the other hand, this would make classes too similar to each other for some players. Unfortunately for me (since I like simpler systems), many people seem to prefer having different ways of relying on skills instead of having more significant skills (i.e., greater bonuses) to begin with.
Like many others, this is an aspect of 5e that works as intended, although it might look a bit strange at first sight. Even if you disagree with some of the designer's choices - and I often do - the results make plenty of sense.