Allowing capitalist relations to persist, even if basic goods like food and homes were nationalized, enables a society in which capitalist profiteers continue to operate. History shows pretty explicitly that Capital will use the levers of power that exist, like The State, to eat away at or overturn any socialistic advances. E.g., suddenly the luxury capitalist corporation that sells idk, pearls, is lobbying (bribing) their way into privatizing beaches from which they operate. Slowly but surely the socioeconomic relations produced under capitalism foment and claw their way back to their former position. This requires a constant, indefinitely revolutionary society to keep capitalist relations at bay; that sort of momentum is not possible to sustain, certainly at the current moment.

It's necessary to abolish capitalists as a class because leaving capitalist systems of relations alone enables them to continue to re-produce themselves.

That doesn't preclude this sort of dual-economic setup from being a good thing, just insufficient.