Labor for anything is expensive in the US.

Parts/materials costs in contractor quotes are often padded so they aren't completely overshadowed by the labor portion. In any job where there's specialized knowledge or license restrictions (HVAC) or risk (walking on a roof), the floor for labor rates is usually 2-4x the materials cost.

But, the real issue is that almost nobody pays cash upfront for their solar install. Between incentives, loans, and/or predatory PPAs, the prices lose touch with reality. See healthcare, college tuition, housing prices, etc. for similar scenarios where credit or third-parties distort the market.