The reason that installation is required is to give users the ability to access applications from within the Google Drive user interface. Without installation, users would have no starting point for most applications, as they would not be able to start at a specific file, and then choose an application.
That said, I realize it can be difficult to work with in early development. We (the Google Drive team) are evaluating if we should remove this requirement or not. I suspect we'll have a final answer/solution in the next few weeks.
Update: We have removed the installation requirement. Chrome Web Store installation is no longer required for an app to work with a user's Drive transparently, but it is still required to take advantage of Google Drive UI integrations.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
