My whm said jsp doesn't work on their economy plan(Shared hosting), take a vps. Why is it so?

I have a domain and we are trying to deploy a webapp we developed to our hosting server. We got economy plan on web hosting provider. Later found out we don't have much of access as well as our JSP files not working and no access to servlet or apache configurations. The support of hosting site said take a VPS. Am bit new to the software field. But why vps for that ?