I gave you my reason why. Cannot help you if you did not like my response.
There are other reasons for five colonies.
* Player wants to tech mine planets with ruins to loot them, and doing so takes months, although the rare items are of little use without other colonies to exploit them.
* Player wants to distribute items over several planets to satisfy demand of his industries without generating too much Pather interest and getting Pather cells implanted on his colonies.
There is no real support for conquering. If there was, there would be alternatives to killing everyone and building new colonies over their ashes. Currently, the player will probably need to grind Ordos for more alpha cores to break the colony limits. It seems more like an accident that conquering in a roundabout way works at all.
What kind of love for exploration? Hopefully, not more FedEx quests or other tedium. Keep in mind anything new and exciting does not stay that way for long.
As for politics, sometimes the player can be forced into it by the constant expeditions and the pather cells. That is a reason why I like to wipe everyone off the map, to eliminate the politics. Unfortunately, wiping out the core worlds does nothing to the Pather cells, which is why I consider Pather cells more obnoxious than Hegemony inspections. I can prevent Hegemony inspections by wiping H off the map, but if I want to avoid Pathers, I need to make sure all of my colonies never grow past size 3 or never get more than eight Pather interests (which means no alpha admin, no hypershunt tap, no more than one colony item on the world).
You have a billion and one mods to get what you want. The most popular mod ever, Nexerelin, is an attempt to turn Starsector into a 4x game.
All I want is to explore and find something interesting. How about unique challenges, or unexpected AI / Alien threats near the edge of the sector? How about more STORY, hints about why the collapse happened, news from other sectors or the REAL core worlds of the old Domain? Unique weapons or items that can only be salvaged from challenges distant from the Hegemony?
To me the magic of Starsector is that the setting is something like a Fallout / Last of Us post apocalyptic world in a far future sci fi setting. There's hints everywhere of a deeper world. As soon as it becomes a "conquer the galaxy" 4x game, the magic is gone for me. What's the point of smuggling, taking missions, surveying single planets, reading the stories of individual characters, if the true scale of the game is being the Emperor of the Galaxy? Emperors don't bother with carrying transport fleets full of organics, or hunting down bounties. They certainly don't care about scanning anomalies in distant remote stars, or stealing transport ships from lightly guarded hangars. If you're Han Solo, stealing a Venture from a lightly guarded hangar is an exciting coup! Your fleet is 25% larger now! If you're the Emperor, who even gives a ***? It could have been a Paragon, and you churn out 5 of those every month.
Btw, your roleplaying exercise isn't just pointless from a gameplay perspective (because every single thing you want to do you can do with one colony or ZERO colonies. You can reopen the gates, murder all the Doritos and burn the entire sector to the ground, with a zero colony playthrough) but is also unrealistic immersion breaking. A game of starsector spans at most 25 years, and every cryosleeper in the game added together makes a single size 7 colony.
Once you've decivilized Chicomoztoc, where is the population of your empire coming from? The Persean sector isn't exactly a beacon of prosperity and growth even in stable times. There isn't enough time in the game to grow the population of the sector in a meaningful way. The fact that you can apparently spring up 2419 colonies or whatever in just 2 decades using AI cores is just immersion breaking, unless in your RP fantasy your colony is entirely populated by androids and AI or something.
Ok one last problem with being Emperor:
It's easy. There is no challenge to it whatsoever. The AI is not tuned like a 4x game, it won't build up to a counteroffensive, reinforce it's planets in times of war. It just.. .Sits there and waits for you to conquer it. It's pointless (there is no gameplay reward for being emperor), it's immersion breaking (because it's impossibly easy to do) and it's just boring. At least a game of Stellaris would be challenging to take over the galaxy, because the game is tuned to make that an actual challenge. You're just farming Alpha cores to plant colony after colony for.. Why? No new items, no new challenges.