Economy of scale has to figure in here somewhere. If an auto company developed a car for a production run of 20, each one would be around $50 million. Make a couple hundred thousand and it spreads the R&D costs out to $5K per car. Companies such as SME, Graham, and Dynavector have been making tonearms for a long time and have a lot of experience they can apply to a new design for free. They're also higher profile makes who sell more copies of what they make. The price difference between a $12K Cobra and a $5K Graham may not necessarily indicate a quality difference if Graham sells ten times as many.
There's also the panache factor. If you're spending $50K on a Caliburn, many customers would expect to spend a proportional amount on a purpose-built tonearm rather than something off the shelf.
