Dependency managers no good.

I have been using composer and bower regularly. And they surely piss me off every time I run them. They download the dependencies each time I run them and then they put them in a folder. The next time I run the same command in some other folder, it picks up some of the dependencies from the cache and the rest are downloaded all over again. Why? Why should this happen? Can't they work the way gems are installed? A folder named .composer and .bower located in /home. And each time I run a install, it will copy the content from these folders. And when I update, it will update the dependencies placed in these folders. Maybe I have been doing it wrong all along, or maybe these managers are actually wonky!