"Question: Wouldn't this make it easier for fraud if fewer votes can be added or switched across the whole country, rather than just in a few states that are required to win under the college model?"
Actually, under the proposed "National Popular Vote" (NPV) system, a lot more votes that could change the winner of an election could be switched in a lot more places without detection. If every vote counted, which seems desirable on the surface, you could switch a few million votes in states that won't audit their elections, and even states that try to detect and correct their own vote switching will have to give away their electoral votes to the apparent popular vote winner -- if they sign on to the NPV Compact.
In other words, even if a state has a squeaky clean election system such as hand counted paper ballots with no voter deception or suppression, they could end up giving their electoral votes to the candidate who loses decisively in that state, but appears to win the national popular vote which is NOT verifiable.
The NPV proposed does not do away with the electoral college; it just tries to get states to ignore it!
As far as who is in favor of this, it's hard to say but I think there are a fair number of uninformed progressive types buying into the one-person, one-vote meme. What they don't realize is that there is no way given our current voting systems to know that the national popular vote tally is correct.
Who else might be in favor it? People who want to steal Presidential elections.