Chimneys deteriorate – typically above the roof, and usually because water is able to find its way into the chimney structure. Then they need to be (at least) partially re-built. This can be costly.
The attached photos show what I like to call “the ostrich effect”. If I can’t see the damage, it is not there!
This chimney was covered with aluminum siding above the roof, presumably to cover up damage to the chimney. The damage will continue, and in fact may now be worse, because the concrete drip cap no longer has the required 2″ drip edge. Rainwater can very easily get in behind the siding, get absorbed into the brick and continue to deteriorate..