Not sure why people are so critical of the sail barge style ship? Yes it has thrusters pointing down but it also has the same engine/exhaust pipe looking thing sticking out of the back as Jabba's original sail barge which looks like it would provide some sort of forward thrust.

As for the design, I would assume the barge and skiffs were not native to tatooine but imports from another planet. It would stand to reason the company that made them might also make other vehicles, so why not a starship? I mean, in real life a company like Bombardier makes airplanes, trains, snowmobiles, etc.

And maybe the skiff guard costumes, since they seem aesthetically similar to the design of the skiffs/barge are typical clothing of the people from the planet where the vehicles are made? Perhaps Jabba's, when he imported those vehicles, also hired some people to help operate and maintain them? And here they are again operating the ships they produced? Seems reasonable.