Problem is awakening a fruit requires the user to be pushed to his limits. The admirals and yonko have great base strength that is supplement by insanely strong fruits even in their base.
Unless they fight each other chances of awakening their fruits are very slim.
There is a reason so far only high tiers (commander level or there abouts) have been confirmed to awaken their fruits. They basically hit their ceiling, the next step is obviously awakening their most used power which happens to be df. The lucky one like Luffy (and Kata to some extent) gets to awaken both fruit and haki since they used both all along.
Not iron clad but this more or less applies to most characters