Because Beth seems to barely think through any design decisions and seem to have wildly inconsistent implementations. Remove athletics skill---"Everybody ends up using it anyways." Change speech so it levels up automatically whenever you sell anything.
This.
The trick to this game is to only put your perks into the skills you want your character to be really good at, the rest is just icing on the cake so to speak.
This is exactly what's wrong with this game. Read what you just wrote. Why are we forced to level skills at all when the perks we place are going to determine the lion's share of our effectiveness with any given skill. If skill level is "just icing" I imagine that Bethesda is eyeballing it to cut for TES VI.
You're certainly not forced to pick every lock or buy and sell every item in sight, or take perks in either skill so I don't really see the problem. Besides occasionally what a Guard might say, but that's fairly minor.
First off, the "you don't have to" argument is tired and a poor defense of any mechanic, and in this case, you pretty much DO have to. What idiot is going to forgo opening every chest he has the opportunity to get at? I appreciated in earlier games how there were at least several ways to get at this, such as open spells, but now we have one option. Second, why are you defending this? Your opinion on the matter is strangely absent from your post, but because you are defending this design decision, it would lead me to assume that you support it, however, you clearly identify where there are issues with the system as it is, so simply: why defend it?
Where is the objectivity? Why must people be so dogmatic in attacking or defending Skyrim? Some stuff in this game svcks, some stuff in this game rocks, can we please stop trying to argue that it is all black or white and just acknowledge that there is a bunch of both? Gah, it's infuriating.