This isn't a port for Finland to export natural gas, it's a barge that's used to receive gas shipments from other countries.

Usually (though not always) the director is the main decision maker and planner, so their time scale of involvement is from the first day to the last day of the project. Most other roles have a lot less time commitment.

Having multiple directors lets 6, 8, 10 or more episodes be created in a given timeframe. Director A can be actively shooting while director B can be in pre-prod and director C can be in post-prod. And all kinds of permutations in between. In planning terms we'd say the director is critical path.

Sometimes people think the actors would be, but they're less involved for pre and post prod, so they can jump from director C's shoot straight to director A's and then to director B's. Often it's not even that linear and there can be periods that overlap.

tl;dr: Directors are critical path, and using multiple directors allow a whole season to be shot without taking multiple years.

Old.reddit.com should fix that up for you