First: the zee-bat has a limited range. It not reporting anything means there’s nothing NEARBY, sure - but it does not mean that you’ve found everything already.
Second: on that note, 4 of the 36 ‘tiles’ that make up the map… do not have actual ports. (I know i hate these) Sounds like you might’ve hit a nearly-full column of these, and concluded that the map was over. It’s not. I point this out because it definitely sounds like you haven’t found a lot of the ports out there.
Third: if you actually have seen most of the ports, take another look at the pages. Two of them, Cosmogone and Apocyan, each have a word in their descriptions that should make a particular port a VERY OBVIOUS option on where to look - if you’ve actually been to those ports. What you’ll actually have to DO there, that’s not as obvious at all. The Peligin page also has a pretty strong hint about one place you could look, but it’s not nearly as direct. Viric and Irrigo don’t so much, but they’re also probably the most common to find even if you weren’t actively looking for them. Gant and Violant, I’ll grant, really are extremely difficult to figure out, and while there are a couple places where you can actually see something violant/Gant available all the time, but are extraordinarily expensive.
Forth: based on what you said about Pigmote, if sounds like you don’t understand SAY (Something Awaits You). There isn’t more story there, no, but depending on who you sided with, you can stop back for really excellent bonuses! A bunch of food, or fuel, or repairs, or terror reduction, all for free, are among the options that might be available, depending what you did (unless you ended up being a colossal jerk and screwing over all of them, of course). It does, however, require SAY.
So, how SAY works: every sixty seconds that you’re out on the zee, there’ll be a bell noise, some flavor text will pop up in the ship’s log, and a lamp icon will appear in the top-right corner of the log. This is all just to let you know the SAY quality is active (if you most over a green SAY icon, active = “stories await you when you next make port”). When inactive, there’s no lamp (and the quality will say “that’s all for now”).
SAY is a random quality (behind the scenes, it has a value of 1-100 when active, or 0 when inactive). A lot of storylets at various ports are “locked” unless SAY is active; others (like Pigmote) won’t even show up if SAY isn’t active. Most of these are just small predictable bonuses - if you’re having tea with someone, you PROBABLY will get some terror reduction, maybe some food to take with you, maybe some information items - but some (usually with “explore” in the title) can have several different events, from little bonuses to rare or dangerous encounters. In some cases, options actually advancing a storyline require SAY. Almost all actions requiring SAY to be active will set it to inactive afterwards. A few options only show up when SAY is INactive; these are generally just you being turned away and told to come back some other time, though.
Fifth: the “become London’s most venerated explorer” ambition IS the one about writing the Zong of the Zee, which is less a poem and more the treatise/memoirs of an incredibly well-traveled zee-captain who’s discovered far more at zee than anyone else. And yeah, that requires a huge amount of knowledge items. If you want a more quest line-y ambition, go for Father’s Bones on your next captain. It’s hard and expensive too, I’ve heard, and probably cryptic at times, but at least it’s structured more like progress towards a goal, with concrete steps to focus on, rather than just a massive list of things without context and you either have em all or you don’t. Right now, the only ambitions are being rich, writing the Zong, and Father’s Bones, though it looks like a couple more are coming out this month?
Fifth: this IS literally a story-based game about mystery, exploration, terror, and survival. Cheesy unbalanced sun-smuggling aside, it’s supposed to be hard and mysterious! You’re expected to die or retire and discover new things on different captains, not find and finish all possible content on one captain. That can be really frustrating sometimes - I’m very much a completionist at heart - but it’s what this game is about, and it’s not going to be something else. MAYBE it just isn’t for you, and sure it has flaws, but do come to the game with that mindset of looking for mystery and discovery. Figuring out how things work is supposed to be part of the fun.