The only reason would be if travel for the Nexus interview would be an issue as you have to go to a Canadian airport or certain border crossings.
GE you can interview at major airports throughout the US.
You can schedule an appointment if you are going to be flying into a Canadian airport or if you are close to a border crossing (which you probably are). My wife and I drove 8 hours to visit a border crossing to get our Nexus vs 30 minutes to go to the MSP airport for just GE. Then we had to get our iris scan at YYC when passing through since the border crossing didn't have the equipment for that. You need the iris scan for using the airport kiosks if you fly to Canada.
I think it was worth it! With Nexus you get all the benefits of GE, easier entry into Canada and it is 1/2 the price! Really the only thing is the fewer places to do the interview.
If you are going into Canada several times a year I say get Nexus for easier entry in, then enjoy the GE benefits when coming back to the US worldwide!