Obama related well to one part of the country, and Trump related well to another part of the country.
Trump's case being more surprising since he's tries very hard to come off as a class traitor. ex. Notice his love of the peoples food (fast food)
The statement that if one can relate to a leader, he will take ones interests more seriously is a strong assumption that I cannot believe in.
Trump is no more a leader to you or me, than Brad Pitt. It's just some person on TV you never come in contact with.
A better question is why is there voting for a president, by people who don't understand anything about what it takes to be good at that job. Absolutely nothing for the vast majority.
For instance, if the president of the country is wealthy and associates almost exclusively with and identifies as a wealthy person, then that person might consider their primary goal as president to promote economic growth as measured by the stock market. Some less well-off constituents might rather the president focused on programs to improve access to food, health care, and education for the less well-off.
This isn't an either-or thing; a president could do both. However, if non-wealthy voters think the president doesn't understand their situation or have any policies in place to improve it, then to that voter is not likely to have a high opinion of that president.