There are locked doors now, why not locked treasure chests (you have to use a key on them before you can pick up whatever they contain).  You could also allow bashing, with a risk that the object inside the chest will be destroyed by the bashing.

Honestly?  Because spending a key to get that weak healing potion on floor level 6 isn't worth it.  chests are 90% useless as they are.  A chest should be limited to a magic item of some quality.  Not random weak potions etc.  Then it would be worth using that key on it.

As it is now, locked chests mean skipped chests.

It sounds like you're wondering, "Why are those potions in chests, rather than just sitting on the ground out in the open?"I have wondered the same thing myself. I think the most likely explanation is that there is some software advantage to using a single image for all random treasure (perhaps it simplifies the code, or perhaps it saves some memory, etc.).

I was kind of thinking in terms of putting more important stuff in locked chests. You might still find good stuff in an unlocked chest, or crappy stuff in a locked chest, just to keep things from being completely predictable, but for the most part the locked chests would have better stuff.

You also wouldn't be "spending" a key to get the contents of the chest. I've yet to break a key, although my characters have all had relatively high agility and low strength, so I don't know how it goes for characters with high strength and low dex. Is it really possible to have a character so brutish and clumsy that you break every key after the first use?

silly me, I forgot they aren't "used" with every door.  that makes it much more palatable.