The court system is designed to optimize throughput at the expense of latency, against the background of a system where authority is vested in a relatively small number of presidentially appointed and Senate-confirmed constitutional officers. About 350,000 civil cases and 65,000 criminal cases are filed every year, spread out across less than 700 district court judges.

To maximize throughput, proceedings are structured like batch processing systems. You submit work, it waits in the queue until the system gets to it, some intermediate decision is rendered, and then you submit some more work. For constitutional reasons, criminal cases cut in line, which can further increase the latency of civil cases. That means that, in a four-year case, the lawyers don't actually work on the case for four years straight. They do batches of work a couple of months at a time, and then work on other cases while waiting for the output.

Moreover, court case are, to a degree, inherently serial. Motions to dismiss--briefs that argue a case must be dismissed because its legally defective--must be filed before you start deposing witnesses or exchanging documents. You generally need to do depositions of witnesses after you've reviewed all the relevant documents. And all the fact gathering must be done before you file summary judgment motions--briefs that argue a case can be decided on the factual record without a trial.[1]

Part of the inherent delay is that the legal system is already an "exception path" in the ordinary course of business. A lot of time is spent waiting for people outside your organization who don't work for you. For example, when you're deposing a witness, they have work responsibilities, vacation plans, etc., and everyone has to work around that.

It's possible to structure cases where everything can be done in a year. That's what happens at the International Trade Commission, for example. Arbitration proceedings can also be structured like that.

[1] This also means that legal teams aren't very big. Massive corporate cases with billions of dollars on the line are handled with core teams of a dozen or so lawyers--with maybe another dozen or two parachuting in to help with specific phases like trial. Technology was squeezed out a lot of the parallelizable work. The days of 20 junior attorneys sitting in rooms reviewing boxes of paper documents are gone.