Drogba leaving for a month is a freaking joke, I don't understand why the club would let him. However, he's not the first one to complain about it and they're right. The MLS needs to fix that if they want to be taken seriously as a top destination. Soccer is meant to be played on natural grass.
Ok, but where do you want him to train in Montreal at this point in time? It's -15 outside.
Edit: I'll precise this post because I find it excuses Drogba. What I'm saying is MLS can't do much about it because even with a traditional schedule, there is parts of the year where, guess what, you have to at least train on synthetic. Also, some clubs don't have the options/control to have another type of surface. Can the Sounders objectively put grass? No, they don't have the final word. I think Portland doesn't have the control on that since the stadium is co-owned with a local athletic club. Does Vancouver have the means to build their own stadium at this point in time?
It's a rather complex issue because not all the clubs are in full control of their destiny. They often depend on another one in another sport or/and have to deal with financial, meteorological, political, etc, constraints.