Same reason there are 2 Disneylands in the USA? (well, one is Magic Kingdom, but it's still the same type of park...)
The rollercoaster in Grizzly Trails sounds awesome. When I first read the description, I thought it was gonna be like Expedition Everest, but with bears... Doesn't seem true now. Looks quite comical (like the track switching to a danger zone after a bear scratches it's back on the signal, or a bear trying to grab hanging fish by dangling out of a hanging mine cart). I think the only similarity looks to be where you go backwards at some point.