The bias towards conquest/expansion is not limited to Civ VI, or Civ games in general. I quit playing
Europa Universalis years ago, even though I love the period and a great deal of the game's elements, but because most of the minor states in the game are inevitably scooped up by the AI or human players until by the late game you have a few Massive Empires dominating the map. Compared to a late game Start in which most of the minor states still maintain some kind of independence, the artificiality of the 'Wide' programming is readily apparent and jarring. The last game, which I ended in the mid-17th century with Europe from the Bay of Biscay to the Balkans divided between massive French and Bavarian Empires with only a few minor powers hanging on between them, was the last straw for me.
Expansion can be limited by various Disorder, Disloyalty, Communication mechanics, but generally that just encourages the gamer to find ways to mitigate them and leaves the AI even further behind the human player. In Civ VI's case that means in the last several games I played (a year ago or more) every game included several AI Civs losing cities to Dark Age/Revolt and several games had at least one AI Civ completely destroyed by losing their Capital to Disloyalty, something I've never even been threatened with as a Human player.
On the other hand, the reality-based mechanics that penalized Expansion were primarily two:
1. The fact that everywhere you went except for the Far Arctic there were already people there, and unless you engaged in Genocide, you ended up with a population that was Foreign and not necessarily happy with your culture/civic/social order. Unless some fairly stringent efforts were made or generations of time went by, revolts were virtually a certainty. And if they had already had a Civ of their own (in game terms, even a City State) the efforts to turn them into copies of your native population were almost certainly doomed to fail: note the obvious modern example of Ukraine, subservient to Russia for centuries yet resurgently claiming their own independent identity now at gun (and drone) point. This was and is a major brake on Expansion: having to spend time, resources and effort maintaining control after spending time and effort getting control quickly limits you to stamping out local fires instead of spreading new ones. Note that of the Greatest Eurasian Conquerers: Alexander and Genghis, the former's Empire fell apart as soon as he died into several separate states and a resurgent Persian Empire within 150 years, the Mongolian Empire started to fragment into successor states within less than 100 years. Quite simply, with the communications and governing technologies and techniques of either Classical or Renaissance Eras it was simply not possible to maintain continent-spanning Empires of multiple ethnicities and cultures.
2. The fact that, as posted by
@Krajzen, most people, including most rulers, are Risk Adverse. And, as was commonly remarked as early as the 13th century, Battle is a Gamble. In a few hours or a single mistake, everything you have been trying to accomplish for decades can be smashed beyond recovery (assuming you, the Ruler, survives at all). That makes Great Conquerers very rare, and even rarer when you factor in the Luck Factor: Alexander was wounded seriously several times, and his survival to age 33 was, frankly, a near miracle. The list of Potential Conquerers that didn't live long enough is much longer than of those that Survived to Conquer - even in Alexander's time it included men like Jason of Thessaly, with all the apparent skills and resources to be another Alexander, but killed by a skull-crushing falling roof tile before he barely got started.
So, how to model the Real factors that affected decisions, and the real problems that dragged conquests to a standstill after scarcely getting out of your homeland?
I suggest one way that I have already posted about: Victory Conditions that reflect how well your Civ did throughout the game rather than how it is doing on the Last Turn. IF percentage of units lost in battles is as important in determining victory as number of battles 'won', the gamer has to think twice about entering battle at all - as the actual Leader his little animation represents had to think. IF number of turns in which half or more of your population is in Revolt matters, you will have to be much more careful about trying to incorporate potentially revolting populations. A continent-spanning empire of seething revolutionaries does not a Victory make, and if political/religious/cultural/social Discontent is modeled in the game and used to calculate Victory, massive Expansion has to be very carefully considered by any competitive gamer . . .