system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why have the civilizations of Star Trek expanded SO SLOWLY?

It seems like the biggest limiting factor is the crystals needed to power starships... but is it really so hard to harvest energy from other sources and store it in some other form (since it apparently is utterly impossible to synthesize the necessary crystals, even if one uses the highest quality replicators and parks next to a star or two)?

If nothing else, couldn't they start spamming colonization pods that basically consist of frozen colonists + industrial replicators + solar panels (or some other such energy gathering device) and just not thaw out the colonists until enough progress has been made for them to live reasonably comfortably?

***

And what about the Borg?  It seems like all they need to do is make ships and... that's it.  They don't even need to colonize planets, do they?

***

And now that I think about it, how has the galaxy not been overrun by sentient machines?  Are they really that rare?  It seems like any race that has overcome the need for colonizing planets, maintaining atmosphere, etc, would have such a gigantic advantage over everyone else that it would be no contest unless they got snuffed out by a more advanced race before they had a chance to blossom.

They could focus on using all their trilithium/dilithium for space travel and use other energy sources for staying alive.  All other resources could be channeled into making ships and reproducing.  Hell, the two need not even be mutually exclusive.
gpt
* Population growth is massive limiting factor, you only really colonize as fast as your population expands (and even then, the need to actually go and settle new lands is low)

* Terraforming is an expensive, long process and otherwise the number of habitable planets actually isn't that massive when you get right down to it, and when you further split things up by travel time and competition from other powers, you get relatively stagnant borders.

* Not everything can be replicated. There are plenty of resources that still require extraction and refinement, and the quality of replicated goods is generally seen as middling. Perfectly acceptable for consumer use, in a sense, but for starships, heavy industrial equipment, really anything that is quality dependent you'll want to use standard processes to produce.