You need to study some basic theory and understand what the Brillouin zone is, and what the K point means. In particular, how the Brillouin zone changes when you repeat the cell. I'm not saying this to be mean, or because I don't want to answer your question, but it will be very helpful for you to understand these points.
The simple (but not so easy) answer is that when you repeat an even number of times, your "K" point is really at the "Gamma" point, which clearly can be seen in your figures (if you calculated the density of states in each case, it would be the same, so the electronic structure really hasn't changed). But, as mentioned, you need to understand why, and for this there are many text books on basic theory of symmetries in periodic systems.
