It's the "$10,000 for knowing which screw to turn" problem. A non-domain-expert (but good general problem solver) could eventually come up with the solution, but they'll take longer. They have to work out a solution either by trial & error (most common) or from first principles (very rare). Either way takes longer than letting an expert look at it and pull a solution seemingly out of thin air, when the reality is it's the decade or decades of experience looking at similar problems that they draw from.