Alternative military transport methods

In the game currently, the only way to transport military units is with transport planes. These also have a range limit, so if you happen to have allies further away from you it can be very difficult to support them.

This made me wonder why this is the only method to transport military units? In real life among many powers that project power, shipping is vital for force projection. The U.S in particular has a large merchant marine force that it can call upon in the event large amounts of forces need to be moved.

While it makes sense for air transport to be an option, Why not have another option that has unlimited range (assuming you reside on a coastline), but takes longer?

It would make ocean-adjacent nations more valuable (i.e competitive) and could help streamline some of the issues with moving large amounts of forces to foreign theaters.

We have recently improved air transport and made it easier.

the range limit is intentional.
we think that being able to transport everything to any place is just too simple.
the range is set to 10.000.
Everything now moves faster too.

We have a plan for sea transport but don't hold your breath.

with a distance of more than 10.000 you need to conquer a country half way, and go from there.