lol... if that was directed at me, then you're under some wrong assumptions about my home! The "newer" doors and windows in the room in which I am sitting now were installed in 1775. The older ones in the room directly below me were installed around 1734. I can see the morning sunlight pouring onto the floor from outside thru the big gap under the door next to me now, and we get SNOW coming in around the edges of the door below me. We have 13 exterior doors and
60 windows, most of which were built and installed in 1775. This house is so "not airtight" that I'd doubt there's a blower door motor powerful enough to actually run a leak test on this big old house.
As to why others aim for air tight? I don't think they do, anymore. HRV's are the name of the game now. People learned their lessons with mold and other problems in the 1970's and 80's, I don't think anyone is going for air tight today, but rather controlled air flow with heat recovery.