“Swing states” do the whole country a favor. They are undecided because their population is more politically balanced than other states. A successful candidate has to bridge political differences and represent the interests of as many different groups as possible. The candidate who can win over the swing states has probably figured out how to represent the most viewpoints across the country.
It’s not as though “safe states” don’t matter in elections. Safe states are “safe” because they have already thrown their weight behind a candidate, allowing that candidate to reach beyond the base and represent more of the country.
Under NPV, “swing” and “safe” would remain in campaign vocabulary. Instead of prioritizing which states to visit, though, candidates would prioritize population centers: Miami, Chicago, New York, Los Angeles, etc. Rather than making elections national and therefore more representative of the entire country, it would severely regionalize election outcomes.
NPV would provide incentive for candidates to target only the most populous ideologies, instead of building bridges and uniting diverse viewpoints. And extremist fringe parties would have a green light if raw numbers—regardless of distribution—were the only requirement to win the presidency.