Why Is there no way to seam meshes together?
Seaming meshes is semi-complicated and has many ways to do it. Are you trying to get rid of hidden faces? Are you trying to just merge terrain together? Depending on what you are trying to do, there is probably a particular way to do it, hence why there isn’t a global “seam mesh” function.
merge terrain together, in a few other engines I have used in the past there is a easy way to do it.
I would recommend you to do that with the world browser: ?v=fUx8vLosDLY (but they will be still two terrains -> I think there is no way how you could connect them -> but you could export both of them as a heightmap and then put them together in gimp/photoshop and import it with a RAW16 file)