Why do we have to capture and convince people to join when they crash land?

[Wintersdark]

Rescue = treat & release
Capture = arrest (with possibility of recruitment)

There are no other options.

in a16, there is a high probability that rescues will choose to join.

[Anomaly]

I've yet to see that in A16, I suppose I was just unlucky. However, in the case of the most crashed survivors, it shouldn't be a chance of recruitment, it should be what happens by default.

They are injured and homeless with little chance of survival on their own. Unless survivors have particular traits or wake to see your colonists eating other survivors, they should want to stay.

It could be that later they learn of family elsewhere and want to leave. In such a scenario, there might be a chance of a colonist leaving - or that colonist bringing his family to the player's colony.