It's a beautiful part of the world. I have walked the walkable bits and talked to the guy who bought Powerstock station at (or I think actually before) closure and still lives there! I hope Sustrans is successful in getting the cycleway complete, because it would make sure that the effort put into building it wasn't entirely wasted.
Extending the service to Dorchester would have made lots of sense, and the double track on the old Wilts, Somerset and Weymouth main line could have been retained as far as Maiden Newton to allow sufficient capacity. But the thinking was all about running down the railways and saving money in those days.
Bridport station was quite a way from the town centre and would have been on the edge of countryside when originally built. Ironically the modern town has now surrounded it. I read somewhere that the council in the 1970s wanted the station site for redevelopment (it's now home to Co-op, Lidl, Toolstation etc) - but with a little imagination a single platform terminus could have been integrated into the new development - maybe even moving it a bit nearer the town centre, sharing the alignment of the old West Bay branch with Sea Road North, built (I guess) in the late 70s.
Thanks to the OP for posting.