24 of the 27 smallest pop states now ignored, could not be MORE ignored.

2016, 94% of the campaign events were in just 12 states (containing only 30% of the country's population).
2012, more than 99% of presidential campaign attention (ad spending and visits) was invested on voters in just 10 states.
2008, candidates concentrated over 2/3rds of their campaign events and ad money in 6 states, and 98% in 15. 
2004, candidates concentrated over 2/3rds of their money and campaign visits in 5 states; over 80% in 9 states; and over 99% of their money in 16. 

There is no evidence to support your beliefs.  In the 4 battleground states that got 2/3rds (176 of 253) of the 2012 general-election campaign events, and a similar fraction of campaign expenditures, campaigns were proportional-to-population in various parts of the states.

TV, costs much more per impression in big cities than in smaller towns and rural area. Candidates get more bang for the buck in smaller towns and rural areas.