End grain absorbs water faster than other surfaces. Pressure treatment protects outer regions of a piece of wood more than inner. To protect the ends of siding, trim and other wood exposed to weather I sometimes use epoxy, or paint. It's tedious and most contractors won't do it even when I pay for it
Howver, I worked with Glen Salsman of Mt. Pleasant South Carolina to do trim in the basement. Within weeks, I had repeated sewer backups and the protected endgrain came through without damage.
TB