Having worked in the market research field, I guarantee you Adidas has tested their advertising before they launched the ads, and has designed them based on the feedback they got from the research. What did that data show them?
Here's a possibility: the kind of people likely to have their purchasing decisions influenced by what pro runners are wearing are already aware that certain pro runners are wearing adidas because we've seen the races live or on tv or seen the photos in news reports. So it is valuable to Adidas to continue to sponsor athletes and increase sales of their product to hardcore participants/fans that way. (they also get valuable R&D feedback from the athletes) But sales to this market segment would not be increased by putting runners into commercials because we already know that Adidas are worn by successful athletes (we don't need a commercial to remind us that haile wears adidas or that lagat wears nike for that matter).
So the market segment they need to attract via commercials is the people who don't follow pro running very closely. Many of these people may be runners but just don't care about it as a competitive sport. Maybe they do care about football as a competitive sport though and have an emotional connection to certain footballers! Or maybe they aren't even runners but want to wear those shoes as a fashion thing and will be likely swayed by what soccer/football players tell them in commercials.
BTW, the adizero line also has football/soccer shoes!