First, the lawyers are not in charge, and were perhaps significantly influential only at certain times, such as at the founding of the US, and in the 60's and 70's. It appears that the people with money are in charge.
Second, lawyers are taught to practice zealous advocacy within an adversarial system, presenting opposing sides to fact-finder. How well this system works depends on the fact finder. In the US political system, the fact finder is the voting public. This fact is why the founding fathers, especially Jefferson, were so keen on public education. An irrational, non-discerning, non-analytical voter pool will be susceptible to unreasonable arguments.
But even when everything works perfectly, there can still be thoughtful, significant differences of opinion. There are often no objectively quantifiable success criteria, compared to most problems in engineering. But even in engineering, there are still non-engineering considerations that set priorities for engineering projects. Performance v. Battery life, for example.
It's why the US system is often cited as the worst way to come up with an equitable governance ever, except for all the others.