They are already striking and attacking the Shikibukai, they can't just say welp retreat.
Order are out, sent and the attacking has commenced
Marines are not coming
You statement makes zero sense for a few reasons
1. Akainu himself wasn't interested in abolishing the warlord system in the first place until he was pressured to do so
2. Anything dealing with kaido and there potential alliance with another yonko outweights the threat of the warlords. Currently the only marine besides drake that knows of this yonko alliance is koby.
3. We are literally shown a panel before of fujitor heading somewhere without giving any context if where he is going.
4. Kizaru chapters ago stated that he had zero issue with akainu sending him to wano
5. If for some reason kuma uses his ability to send sabo and the other Revos that were with him including bonnie who was also in the holy land to wano, if that info is leaked to the world government you think they wont proceed to wano since they already have newspaper printed more than likely implying sabo was captured?
Again these are only but a few reasons why akainu would order the marines to retreat and focus there attention to wano