I think either “to” or “on” would be acceptable in that context. English likes to use “to” with attention, like in the phrases “pay attention to” or “draw attention to”, often emphasizing the change in focus. But you can also keep your attention “on” something.

As a native English speaker from the US east coast, I would probably have chosen “on”. Just sounds better to me to use “on” instead of “to” when there is no associated verb like “pay” or “draw”. Not sure why.