You mean the author of haruhi? lmao I guess they just get bored of thinking what to do next when there is nothing left to tell, like with haruhi, she is the literal fabric of space and time, how do you create a path where it ends in a good way for everyone? The same with this one, alex is literally a god even if he dies, how do you try and make a satisfactory ending? I guess you can do like the author of the exiled guy with the moms of the party members where you continue beyond their ascend to godhood but it just becomes boring after that...
I am a believer that if you want to write a novel at least have a start and an end, what comes in between is up to your writing abilities, just don't be like akasaka and fumble that path together with the ending lol