On headphones, even the more expensive ones, why do they keep using this horrible fake leather, that disintegrates after just a few months of use?

How else are they to get you to buy now ones???

On real headphones that part is replaceable.

I have two cheap pairs of headphones, both of which I wear daily (one in the workshop, the other while at home and outside) and both show not any signs of wear and tear (both get sweaty ear cups (on-ear) when the weather is warm, but still, they stay good).
I have one pair that’s slightly more expensive, but I don’t wear that one enough to see how fast it’d desintegrate.

Perhaps it is a lotion you put on your hands, or a cleaning solution that deteriorates the material. I have never seen this issue of which you speak, and I have two sets of headphones.

It has happened to every single pair of headphones I ever had.
It happened to my office armchair, too.

Where on the headphones does the problem occur? You should decide whether the problem is caused by perspiration or the friction from handling. If the disintegration is consistent across brands (the fake leather deteriorates in the same places regardless of brands), find a set of phones that excludes the phony leather

Well, when you sweat acid that is a negative consequence.

Depending on how often you wash your hair, if not daily, the natural oils in your scalp/skin could be causing the problem.
Where on the arm chair did the problem occur, specifically?