Most commonly data is centralized in a database or somewhere. This is helpful as it doesn't matter which computer or device a user is using, they get their data. Accessing this is most easily done server-side, and from a security perspective means you don't have to open your database up to anyone on the internet (at least directly). There are JavaScript libraries that could do this, but imho JavaScript is no where near as nice as c# or vb.net via the asp.net framework.
In mvc the standard aspx view engine is to my eyes far closer to standard asp. Mind you in those days I recall using response.write a lot. I find razor simply has less mark-up, so to my eyes views looks less confusing and intent is clearer. I found the transition natural to razor, but really it is preference as some people appreciate the more mark-up in vb.net over c#.
