It's epistolary: the protagonist begins the novel writing as he would speak. He has no idea anyone's actually going to read the logs.
I "got" a different opinion in that he does seem to at least hope that someone will read it. It will/should be discovered when the next mission returns to Mars regardless of whether he is still alive or not. He takes great care to tell those who left him it was not their fault and he also speaks of trying to make it understandable by any laymen who might end up reading it.
He also is a botanist as well as a mechanical engineer so obviously well educated. So would he really speak this way? Perhaps he would as I do know fairly well educated folks who tend not to show such through their normal speech. However, he is writing this with the stated hope and possibility that it will indeed be read; otherwise his time could be much better spent on the things he is actually writing about doing in order to survive.
Regardless of his speech pattern, that is not what makes it a difficult sale in my view. I think the logs could well be incorporated by spreading them out rather than all at once in order to bring more action/drama/hook at the beginning. For instance, the story of how he was actually stranded could be told through normal narrative as well as inner thought to better effect imho. He could even bring in dialogue from his last communications with the others as well as futile attempts once he was cut off. That could increase the tension and show some small character traits of the others while trying to rescue or decide to abandon him.
At any rate, it is hard to argue with success and my hat is off to anyone who pulls it off, especially if it was indeed initially self-published. I shall have to read further based upon your report of later chapters. Take care. Vern