By designing maps for specific modes, you can properly tweak the maps accurately to achieve balance and a more solid gameplay. The terrain can be altered accordingly without having to consider other game modes on that specific map.
As an example, "Isla Inocentes" from Bad Company 2 is an asymmetrical and a linear map, perfect for the game mode rush, where the attackers has access to a variety of vehicles and the defenders have access to stationary weapons and the defender's advantage (Force Concentration). Using alternate and flanking routes instead of the "main path" is encouraged, as it opens up opportunities and different angles of attacks.
In first base, the attackers can take transport helicopters directly to the enemy base (the first 2 green dots in the island), leaving them rather exposed to a lot of fire from a number of angles. However, they can also take patrol boats and attack them frontally or circle around to the back of the island using a smaller but faster jetskis. Alternatively, the attackers can walk and take the main road on the right, swim across and attack them from the flanks, where enemies won't typically be paying much attention to as the main attack will come from the south. Carefully placed ledges and details that smart players make use of can give tactical advantage.
But that's the first base alone. Isla Inocentes is a three base map, with each base requiring different tactics and angles of approach to accomplish.
Aside from the gameplay, this can also improve immersion. Taking Conquest as an example, the game's description originally describe it as 2 sides fighting over resource points mining for Germanium (they changed the description)
On maps like Tourmaline, Therma or Polar, this makes sense (kinda). However, on maps like River City or Crimson? That pretty much kills immersion. Why are people mining Germanium in a middle of a street? Why is there a resource harvester in a middle of a platform above a railway? I know Logic is LosTech, but that doesn't mean we can't improve immersion.
Does anyone know why pilots are fighting in Grim Plexus or why Viridian Bog is so important that they had to send a Mech Company to fight over it? All it is, is pretty much where a massive insect died.
The map from my previous example, Isla Inocentes has the attacking team destroying an artillery base that the defenders are trying to protect. By destroying the artillery base, they could then successfully move inland safely. If they fail to destroy the base, the defenders will then launch artillery strikes on the ships out in the distance. You don't need cutscenes to tell what's going on. Map atmosphere, scenery and mission objectives alone tells the story.
Of course, maps like Crimson and HPG (especially HPG) also somewhat tells a story. Control of the port in Crimson along with the railway will provide logistical advantage, and thus would be worth fighting for. Control of HPG Manifold will allow for communications and whatever the HPGs are designed for.
So now imagine River City being remade again as an Escort exclusive map. It will be asymmetrical and linear as it should be since the game mode is asymmetrical with both sides having different objectives. The escorts will start around the port and would be forced to protect the VIP/Objective until it reaches the runway/airport on the other side of the city. You can add immersion through dialogue and set pieces and have something like the Escorts stole some prototype weaponry from the shipment in the port, and mounted it on the VIP Atlas then escape on a hijacked dropship waiting in the runway.
Even as simple of a scenario like this will add immersion as to why you're tasked with protecting/intercepting the VIP, rather than escorting a random Atlas into a random square on some random place of a map.
Eh. Juuuust a random thought dump at like 4AM in the morning