Someone, I can't remember who, explained it better than me, but the gist of it is by not voting, you are effectively checking yourself out of politician consideration.
If we see politician as just a machine who's only job is to get elected, they have to get as many votes as possible. Pandering to the individual is unrealistic, so you usually target groups of people who share some common interest. As your aim is to get as many votes as possible, you will want to target the “bigger” (in amount of potential vote) groups. Then it is a game of trying to get the bigger groups which don't have conflicting interest.
While this is theory and a simplification of reality, all decent political party do absolutely look at statistics and survey to for a strategy for the election.
If you are part of a group that, even though might be big in population, doesn't vote, politician have no reason to try to pander to you. As a concrete example, in a lot of “western” country right now, a lot of politician elected are almost completely ignoring the youth. Why ? Because in those same country the youth is the age group which vote the less.
So by not voting, you are making absolutely sure that your interest won't be defended. You can argue that once elected, you have no guarantee that the politician will actually defend your interest, or even do the opposite (as an example, soybean farmer and trump in the U.S). But then you won't be satisfied and possibly not vote for the same guy / party next election (which is what a lot of swing voters do).
But yeah, in an ideal world, everyone would vote, see through communication tactics and actually study the party, program and the candidate they vote for, before voting.