1. You get less information at the top of each diary, because of the Annoying Space.

2. From a graphic design POV, it makes the main content look like it's huddled up against the left margin. It also means that bilingual diaries have two big and two small columns next to each other, which isn't very easy on the eye.  

3. There are two adjacent lists to navigate, and they're out of sync. Single linear lists are much easier to read through and navigate than paired but unrelated lists.

4. Balancing the links across both sides also solves the I Hate This Space problem, because it's not hanging around being annoying any more.

Example 1

Example 2

(I haven't stretched the top right in Ex 2 so the top isn't aligned, but it shows more or less what the 2 column option looks like.)