flies on my chrysanthemums

Not sure if this is really on topic, but it's a question about living things in a city....

We moved into our new rental house in June. It has two chrysanthemum plants in the front border. I've noticed that the mums have a zillion flies on them whenever I walk by, and the flies are not on the other plants to the same degree.  Why would flies love a chrysanthemum?  I Googled this morning, and the results that appeared seem to indicate that mums tend to keep insects away, not attract them. These flies look like houseflies, about 1 cm long, not tiny gnats. I do have a hummingbird feeder filled with sugar water, but it's hung up a couple of yards away, not directly over the mums where it might drip on them.