Regarding your edit: This might be the reason, why people tend to vote against their interests. To weed out competition. For instance, people would happily vote against free school lunch - even if the option of free school lunch would benefit them - just because some different ethnical and/or political group would not receive that benefit either.

I see a very similar behavior in German politics right now: The right-wing party (AfD) is gaining popularity and the conservative party (CDU) is going to lose voters towards them. In order to appeal to voters they want to (very oversimplified) alter social welfare benefits to the worse and keep minimum wage from rising, all while claiming that immigration (among other things) is the issue. But those who are voting for the right wing party and the conservative party as well are the ones who clearly would benefit from better social welfare an a higher minimum wage. These people would rather decline any improvements regarding social welfare and minimum wage, so that others (immigrants for example) would not benefit from them either.

Edit: typos