I hear this a lot, but I don't think it makes any sense.
If you have a national popular vote, the "states" don't matter. At worst, you might see a concentration in media markets.
On the other hand, every vote matters, so a vote in North Dakota is just as important as a vote in California.
In today's world, candidates don't buy much national advertising, because reaching every single American is expensive, and most of them don't matter for electoral purposes. Only swing states matter, so candidates only pay attention to people in those states.
If there is a popular vote system and they end up focusing on places where there are large concentrations of people, that's ok, because there are large concentrations of people. If 10 million people have concerns, that really should trump 1 million different people with different concerns. Nevertheless, every single voter with an issue is a potential vote that matters in the election. Candidates couldn't afford to ignore anyone in a close election.