It's likely because the brand is dead and they don't likely give a f about a 19 year old factory radio setup since it won't make them much money so they do what they can to avoid messing with it. Just another thing to deal with owning an old car.
Worst case you can surf Crutchfield and find something better (with premade harnesses and retain the PAC/SWC functions) and have a nice modern system. Just a thought.