Question: Can any chess engine tell you why a move is bad or good? For example, say a chess engine says the score against my opponent is currently +2 in my favor. I then make a move and my score drops to say 1.4. Can any engine tell me what I did wrong such that my score dropped from 2 to 1.4 (assuming I didn't hang a piece or pawn etc.) 

It seems to me that having chess programmers make their programs even stronger is now pointless and it would be much more beneficial to the average chess player if they could have their programs instruct us why a move is bad (or good), assuming they currently cannot do this.

Answer: 
I think the chess engine can "tell" you, but in an indirect way.

What I would do is to play several different moves from the same position. The chess engine will (presumably) give you a different score for each one.

This will allow you to "rank" the various moves. Perhaps a pattern will emerge. If not, you might want to get a (stronger) human player to explain the chess engine's rankings to you.
The engine evaluation ("2"/"1.4") is in fact very similar to how a human would evaluate a position. It is basically a sum of various factors such as *material*, *king safety*, *piece activity*, etc. evaluated not for the current position but for the position some 20 moves ahead or so; assuming perfect play from both sides.

In principle one could try to monitor the change in all those factors separately (instead of only their sum as engines do). For instance if a move leads to a lower value for "king safety" later on compared to the best move, one might be tempted to tell the learner something like: *Your last move made your king more vulnerable*

However I doubt that this would work in actual games, because:

* the learner's move might in fact have other issues: for instance it might neglect development and only because of this the player might have to make concessions later on regarding his king's protection (assuming best play).
* many factors might change at the same time, some going up some going down for instance. Trying to express this in words might be cumbersome, e.g.: *Your last move neglected king safety, but improved your piece's activity and you lost a pawn but occupied an open file* Would this information be helpful to a learner?

Because of this, I doubt that computer's will be able to teach you positional or intuitive play (based on principles) at least with current technology. Better to use classical methods such as other humans, reading/watching/listening annotated games, etc