The difference is location - Niagara Falls Canada is in one of the warmer areas for Canada so it has expanded for tourists; It also has the better view of falls.
I know dozens of places there. We brought a friend on a trip once and I surprised her stopping at a Buddhist temple, one of largest in North America, She is Buddhist and had no idea it was there.
There is no reason to put a lot of tourist stuff for American Falls - some hotels, some places to eat and view of falls. Hard to find reason to invest at that level there.