I suspect that a photo opportunity/day was a very special occasion, a historical event.  As such they wanted to look their very best.

I once asked some relation why he always wore more dressy pants than blue jeans.  He asked if I compared prices, he could not afford blue jeans.

HERE blue jeans are common in church, at funerals and etc.  "Being there" should be more important than getting all gussied up in ribbons and bows attempting to hide the real you.  Some people would never recognize me in a suit, though I wear one once in a while.  I wouldn't want the grieving to feel that someone had signed the registry to make it look like I had been there.  :-) 

Beside, "business men" do not dress up better than in their "work clothes" for special occasions.  I do. 

Great pictures.  And yes I have noticed the same thing about old pictures, those generations.  They worked hard but apparently made the time to present themselves well.  We are too busy to care.