Why do I need to create an IOTA instance to use the library functions?

Question

Let the IOTA node instance be iota variable in the following context:

var IOTA=require("./node_modules/iota.lib.js/lib/iota")
var iota=new IOTA({ 'provider': 'https://iotanode.us:443'})

If I want to make a digest of a SEED="ABC...XYZ", I do the following:

var digest=iota.multisig.getDigest(SEED,0,2) // Retuns the digest as a string

Why do I have to use the IOTA node instead of the library functions themselves?

For example:

var multisig=require("./node_modules/iota.lib.js/lib/multisig")
var alt_digest=multisig.getDigest(SEED,0,2) // Retuns and Object

I know that when I use getNewAddress() it will use the node to get a valid one, but why can't I generate a digest without a node?

Thank you.