Maybe in the future they will allow actual base building to establish a meagre outpost far away from the bubble, then have this colonisation to nearby stars with the gal map blue line from that, and maybe this current blue line only colonisation is just them testing that. I imagine that establishing a base out on the sticks would have to be a mammoth undertaking to stop random bases popping up everywhere overnight. Anyway, I know this almost certainly is not what they will implement, but it would be what I'd do with the game. As it stands, gradually extending from the bubble only seems to be a bit of a waste of time.