Because GMs are stupid and aren't as analytically driven as fans are. I think it's really easy to understand how it happens, because a majority of GMs trust the eye test more than analytics. It's not like JR had a senile moment and was the only guy to offer anything to Johnson.
Look at what GMs are in the NHL today, I would say there are 3x-4x as many GMs who were GMs in the 1990s than GMs who joined after the analytics boom in hockey. It's not surprising that these things happen all of the time in the NHL when you consider that JR, Murray, Holland, Lamoriello, Bowman, Poile, Wilson and Armstrong are GMs in the NHL today.
Want to know why guys like Staal, Gudbranson, Daley, Girardi (both pre and post buyout), Johnson, Scuderi, McQuaid, Polak and Phaneuf are still around/stayed around way longer than they should have? Because most GMs don't use the stats that fans use to show that these guys suck.
Oh yeah, he has done a really terrible job with winning 2 cups for the Penguins.