It looks similar because there were and are constraints on locomotive design, whether steam, diesel or electric. First engines designed for the same purpose, in this case light duty shunting are going to be similar in size, weight and wheel arrangement. There are also clearance constraints to be considered (Known as loading guage in the trade) ,the dimensions of all vehicles using the railway must be such that they will clear all obstacles, bridges, platform edges tunnels etc. etc. If engines were bought off the shelf from a builder then they would be virtually the same, the only differences being in colour and style of livery.Engines by the same designer would have a "family resemblance", as would engines belonging to the same railway company.
