Well it is true that the American weather is good and the site of the place where the world cup would take place will be quite better with no big restrictions like what happened during the last world cup that people where restricted from drinking beer and other beverages because it was against there law.
Making two countries to host the world cup is a bit very rare to me because I don't think this had been happening before. What I know is that it's only one country that normally host the world cup. Now it would involve two countries.
I remember that after the Korea Japan world cup FIFA was very adamant about the world cup never being hosted by more than one nation, but with the increase on the number of teams, games and stadiums needed for the next world cups then FIFA had to reconsider their posture, so I think that from now own multiple hosts will become the norm, after all if the US cannot host the world cup all by itself then who can?
We had the world cup with two hosts before if I'm not wrong but still, we never had three countries in a world cup however America is the primary host and Canada/ Mexico are just helping America but I think the reason of why FIFA made three countries hosting the world cup was increasing the number of teams in the world cup that's why we need more hosts instead of one country hosting the world cup.