But it would be really interesting, if there were other possibilities too we could think of.
A hundred years ago nobody thought something like quantum entanglement could be possible. Maybe there will be a similar eye opening surprise in extra terrestrial life.
But off course it’s reasonable to start looking for all the things we can already imagine, and make observations in a way we already know of.
We simply don't have a framework other than basic physics and chemistry to speculate in this area. The possibility space is too large and we don't know the fitness function.