Heart disease and cancer have a steady demand for ICU beds at a population level (maybe a little bit peaky for heart disease around stressful times of year like DST changes and family gathering holidays), so demand can be forecast and supply can be adjusted over time to meet the demand.

OTOH, a pandemic with high peaks of demand is hard to plan for. And having excess capacity on hand for such an occasion is hard when everyone is always upset about how expensive healthcare is.