Good point. The focus did seem to be more on spiritual transformation. The way that the Romans were, it's probably because He didn't want to be crucified before his time. Seems to me, Him and his disciples had to tread lightly.
There is always more than one thing going on, and for sure Paul did not want Christianity declared a menace to Rome (at least not for any reason except the gospel itself).
In fact, Paul's teaching (and the OT as well) clearly made slavery a practice that was not compatible with the pure Christian lifestyle. The early Church had realized that, and the Church realized it again in the latter 1600s. Except for the small region of the American southeast in the 1800s, the Church had never validated slavery in doctrine. It was considered within the authority of earthly kings (Romans 13), but was always considered a vice in Christianity. To this day, Christianity remains the only religion that has created an anti-slavery doctrine.
However--and this is my point--it is a doctrine
by Christians for Christians. Even as Paul invalidated it, he invalidated it for Christians and within the Church by a Christian argument (Ephesians 6:9, in particular). In the same way, making sure everyone is cared for by the giving and sharing of the resources of our common Master is also a doctrine by Christians for Christians, as we see practiced in Acts 2 and Acts 4.
If we actually think about how the sharing of resources in Acts 2 and Acts 4 had to be executed. How did it actually operate that people's needs could be met...that required a great deal of
knowing each other's personal affairs. That is not a relationship with the world, but a relationship within a Body. Paul gets into even more details: Everyone has a resource, everyone has a need, and resources are shepherded to efficiently meet the needs.
We even see this in the distribution of manna in the OT. God specified the need: One ephah per person. Then as the people collected the manna, some collected "much" (more than an ephah) and some collected "little" (less than an ephah). But when the total was measured out ("meted" in the KJV means "measured") it came out to one ephah per person.
This stewardship requires the shepherd knowing which are his sheep, which is a reason congregations should have membership rolls. As a pastor once said to me, "I will be held accountable to the Lord for how I kept His sheep. How can I be held accountable if I don't know who they are?"