Every author has their own motivations, but I will echo what the parent has expressed that often, if not the majority of the time, authors are making their papers far more difficult to read than they need be.
To that, I'll add anecdote. Some years back, I had a fight with a coauthor on a paper who wanted to remove the majority of the substeps within a proof. He believed that it was condescending to include such material and that any interested reader should be able to derive it for themselves. And, in fact, he asked a colleague in the room at the time who agreed with him. I stated flatly that as the primary author that I could not understand nor complete these proofs without these steps, so the material stays. I contend that at least in this one particular case a combination of exclusivity and arrogance led to an attempt at obfuscation.
Remember, publishing isn't just about sharing knowledge. It's also a way to posture, advertise, build a brand, and get grant money. Beyond that, mathematicians are still people with all the imperfections that implies.
To that, I'll add anecdote. Some years back, I had a fight with a coauthor on a paper who wanted to remove the majority of the substeps within a proof. He believed that it was condescending to include such material and that any interested reader should be able to derive it for themselves. And, in fact, he asked a colleague in the room at the time who agreed with him. I stated flatly that as the primary author that I could not understand nor complete these proofs without these steps, so the material stays. I contend that at least in this one particular case a combination of exclusivity and arrogance led to an attempt at obfuscation.
Remember, publishing isn't just about sharing knowledge. It's also a way to posture, advertise, build a brand, and get grant money. Beyond that, mathematicians are still people with all the imperfections that implies.