More robust capacitors exist. They just cost more. In HVAC world, the practical differences between a motor start cap and a motor run cap are price, physical

More robust capacitors exist. They just cost more. In HVAC world, the practical differences between a motor start cap and a motor run cap are price, physical size, and longevity. A start cap is cheaper, but is meant only for intermittent duty and is unsuitable for use as a run cap. Meanwhile, a run cap costs more but can serve as a run cap or a start cap. All things (except for outliers like the McLaren F1) are built down to a price.