One of the goals of the game design is to focus on the grand sweep of future history, and avoid being bogged down in the usual tarpits of the genre, such as:
- Manual placement and management of planetary improvements. Often times the player has to micromanage the development of individual planets, by balancing space farmers vs space miners, placing down the appropriate number of space farms and space mines, and then replacing/upgrading structures as new space farms and mines become available. This process is time consuming, requires micromanagement, and is ahistorical. Additionally, it rarely raises interesting questions, since most planets will develop along similar lines, and the decisions needed usually boil down to very simple heuristics. At its worst, this design problem progresses to Moons Disease, where the player has to order the construction of new space farms on each of their moons of each of their planets in each of their systems.
- Ship customization and tactical battles. While these are potentially fun, and can be great games in their own right, I think they are ultimately orthogonal to the experience of leading a space empire. And when ship design and tactical battles are done badly they can sink the rest of the game too. For instance, many space 4X games have a great deal of micromanagement associated with ship customization. You might have to upgrade all of your ship designs to use Lasers III instead of Lasers II, and then individually order the refit of all your existing fleets. Another common problem is that when the tactical battles are broken (either due to AI weakness/bugs, oddities in the auto-resolve algorithm, or other factors), it breaks the strategic layer too. If the AI can't win an even battle at the tactical level, then it will need additional bonuses at the strategic level. And if the AI already can't play the strategic level as well as a human, it will need yet more bonuses on top of that. This leads to situations where in order to be decently challenging, the AI receives massive bonuses at the strategic level, produces absurdly large armies, and is basically no longer playing the same game as the player. And at that point the player is no longer playing the game as a thematic experience, but rather as an exercising in taking advantage of the AI bugs. By removing the ship customization and tactical battles, we remove a common point of micromanagement and design failure.
Incremental technology advancement. Often times sci-fi games have numerous tech advancements which yield only small, incremental effects on gameplay. For example, Lasers1 Tech gives +10% damage, Lasers2 gives +20% damage, and so on until Lasers8. Another common variant is SpaceFarm1 gives +1 food, SpaceFarm2 gives +2 food, etc. These sorts of techs are usually bad in sci-fi games for a couple of reasons. One, they don't create very interesting choices for the player. They may slightly change the math of the existing choices, but they don't change the decision landscape or ask the player to think about the game in new ways. A second problem with these incremental techs is that they do not convey any thematic flavor. You can add a tiny bit of flavor through the tech's text and imagery, but if the effect of it is just making a weapon or farm 20% more effective, then it doesn't really say anything about what is going on in the game world. This is a particular problem in a sci-fi game, where you want the factions to be as alien and different from each other as possible. When you think of a sci-fi universe like StarTrek and the factions in it, you don't think of them as "oh, the Federation gets +10% food from farms, and the Cardassians get +15% damage from lasers". Rather, you want something like "oh wow, their ships can turn invisible and we have to scramble to deal with that", or "hmm, they are self-replicating robots and don't eat food at all.". I think those statements are much more interesting both from a gameplay and a thematic perspective. Also, they involve less micromanagement, which is one of the goals of the design.
I do think that incremental techs can work in other games though. For instance, Victoria II is largely about the process of industrialization, and involves similar societies at similar levels of development. So in a game like that, more incremental techs make perfect sense, and they act kind of like the loot chase in an ARPG, drawing the player along.