If three helium nuclei combine to form a carbon nucleus, energy is liberated. Why can't helium nuclei combine on their own and minimise the energy?

Helium nuclei combine to form an oxygen nucleus. The energy released in the reaction is if m_(O)=15.9994 "amu" and m_(He)=4.0026 "amu"

Helium nuclei combines to form an oxygen nucleus. The energy released per nucleon of oxygen nucleus is if m_(0)=15.834 amu and m_(He)=4.0026 amu

When two nuclei (with A=8) join to form a heavier nucleus , the binding energy (B.E) per nucleon of the heavier nuclei is

Hydrogen nucleus combines to form helium then energy is released. Binding energy/nucleon of He is greater than hydrogen.

If a star can convert all the He nuclei completely into oxygen nuclei. The energy released per oxygen nuclei is (Mass of the helium nucleus is 4.0026 amu and mass of oxygen nucleus is 15.9994 amu)