Presence in the courtroom is kind of a red herring. It's uncommon for cases to get that far.
The real costs come from the US legal system being originally designed by and for agrarian villages of Saxons arguing with each other about who stole whose sheep, with the process handled in a more-or-less ad-hoc manner by village leaders for whom it's mostly a side responsibility, and the whole mess serving double duty as a source of community entertainment not unlike modern reality television.
A lot has changed over the past 1,000 years, but at it's core it's still a system that puts an incredible amount of focus on people arguing about Every. Single. Damned. Thing. No. Matter. How. Trivial. The really expensive parts of a lawsuit are the parts that create the most opportunity for this kind of bickering. Which is typically the parts that don't happen inside a courtroom. For example there's the discovery phase, which all by itself is so unusually complicated and expensive that it's spawned an entire multibillion dollar industry that basically only exists in English-speaking countries. And all the ancillary litigation over nitpicky procedural matters. And maybe other things, but those are the two that are the worst for being inherently expensive, easy to weaponize, and peculiarly Anglo-Saxon.