It's rare to see rich billionaires, no matter how old, who aren't keen to make more money. And as Pexbo said, there's obvious benefit for the INEOS brand in being associated with United. While United may become INEOS' highest profile asset, we're far from their only one, and those others were pursued with clear business rationale too.
The key point is that not only are neither of those objectives are at odds with the development of the football team, they are aided by the football team doing well.