We already have Google spreadsheets and many more such apps/web apps. Why would someone jump to this?

I think you need to clarify more about your USP. Becoming more specific about your functionalities such as what kind of security or what kind of user permissions, etc. might help you gain more attention.

People already have such apps/web apps available. So, you need that one wow factor to make the users jump from one service and come and use yours. Try to think more from an user's perspective and try to redesign the way your web app is going to work or help companies/individuals in handling spreadsheets with ease. Good luck! :)