There actually has been ..BUT, many go unreported...per a good acquaintance that does a lot of back country work on horse for the forest service..many of the locals have regular run ins with them ...not always physically attacked..other issues...also YNP has had several deaths in the past decade..but the greenies don't want to reflect on that..

Examples:

https://www.yellowstonepark.com/news/man-killed-by-grizzly-yellowstone

https://www.backpacker.com/news-and-events/grizzly-bear-mauls-three-kills-one-near-yellowstone

http://www.foxnews.com/us/2016/06/30/sheriff-grizzly-kills-person-near-glacier-national-park.html

http://www.bozemandailychronicle.com/new...1cc4c03286.html