Efficiency (in time and space). You can build a simple machine that finishes the task in five slow hours or you can parallelize, stack, route, etc. it and do it in a few minutes. Kinda a programming/logistics game in that regard, IMO.

Even in similar games like Dyson Sphere Program, you can play with cheats on (infinite or free resources) and but it's still a challenge to scale up production.

If you play on the harder difficulties, you are limited by the number of platforms you can build (even if you later delete one). You earn more by delivering certain shapes, with more complex shapes giving more points. It means your platforms both need to be efficient, and you need to be thoughtful in how you place them.

And blueprint points (which are used for copy and paste as well as placing actual blueprints) also need to be earned by building particular shapes.

> What is the motivator of the primary gameplay loop?

For me, it's about my intrinsic motivation to come up with cleaner/simpler machines that are nonetheless efficient. MAMs ("make anything" machines) are a pretty damn fun challenge to build efficiently.

Whenever I play Factorio, I play with the Biters turned off. For me, it's about managing the throughput and the aesthetics of the factory I'm building.

I still run out of resources, but typically by that point I have enough stuff that creating mining outposts is trivial, and in fact significantly better - I get trains full of raw ore, iron plates, and steel instead of having a big chunk of my primary factory devoted to processing that stuff.