Caller ID Name (CNAM) is not sent over the public switched telephone network with your call. It is looked up by the called party's telephone service provider, using a database of names matched to numbers. There is a cost to maintain these databases, and, since Google Voice is mostly free, Google doesn't feed its users' names and numbers to the databases.
The field you are filling in is typically only used for calls that travel from one SIP service provider to another, not over the PTSN.