Having a large fan base will be one factor as it will increase the exposure.
United v Liverpool will always attract good viewing figures for example worldwide.
I don’t think we have that just yet and if it was a 7th v 8th game, we would not get as many (or even a 1st v 2nd game with those 2 clubs I think more could watch). But that is not what is happening.
Success and the importance of the game we play in means that this year we must have played (and won) in the most viewed games.
City v Arsenal
City v United (FA Cup)
City v Real (CL semi)
City v Inter (CL final)
All my United/ Liverpool friends watched all of these games (probably hoping we lost).
But these are some of the biggest, most viewed games across the whole world this season.
The constant in that is City and also City winning, a sponsor would love to be associated with that.
The eyes of the footballing world have been on us this season.
To also take your view one step further (although not sure this is true anymore, I think they hate us with a passion).
As we a told our winning is hollow and no-one cares then our sponsors have all the exposure with no downside.
Where you speak about United fans not buying Team Viewer etc. just as they are sponsors. I can tell you my Dad would not buy any product associated with United (because he hates them). So if they where sponsored by Etihad and he wanted to go Abu Dhabi he would fly Emirates and take the hour commute.
Although he might be a unique case :-)