The reason is right here: Sea routes as we have them are terrible, the suck, they destroy way too many strategic points, allow backdoor entrances into cities, are not actually anything even resembling sea, and they're an ugly hack. That is why I don't want proliferation on them.
And not one single bit of this is a good counterargument to all the reasons—stated pretty well in this thread, so I'm not going to repeat them all—why there
should be
just one more sea route on Beluaterra, after the biggest change to a continent's geography in the history of BattleMaster has happened and left one part of the continent extremely isolated and likely to end up way less fun than most of the rest of the game without such a route.
