Mars might have the most advanced shipyards. They're also building the new fleet for the evacuations, and if the Romulans saw that as an invasion fleet instead, they wanna target the facility that built this fleet.
In Unification, the Romulans used the pretense of a peace mission to send an invasion fleet in stolen Vulcan ships. This is their way, so they wouldn't trust Starfleet, cause if the situation was reversed, they would have invaded. Garak was right: The Romulans didn't believe the Dominion's innocence, cause an invasion is precisely what they would have done in their place.