Makes sense for us, but not for SE. The purpose of the system is to keep us running the instance, so that there is a constant pool of players who want to run CT. If you could just run it once for the week, get your one piece of gear and then be done with it, many people would stop running it and your pool of players would shrink. Not to mention the content would be less utilized.

Now, you could make it where each boss drops a coin and you have to win that coin from each boss. Now you'd have to keep running it, each boss, until you acquired all four coins. Not sure if this is any better or worse, given you could be in a position where you have to run it a significant number of times until you can acquire all of your coins, unless you had an FC running with you regularly.