Throne vs. Camilla .... Throne & Camilla
It seems quite clear that the Saxe-Coburg-Gothas (er, Windsors) found Camilla unsuitable then, and that Charles felt unable to marry her with family approval.
So Charles drew two history lessons. Like his great uncle, Edward VIII, he could not expect to be king with a wife rejected by the establishment. And like his Aunt Princess Margaret, who called off her wedding to Peter Townsend, Charles faced a certain ostracization from his family if he pursued his true love.
Presumably, then, Charles either felt unable in the 1970s, or knew it to be an impossibility, to make Camilla Princess of Wales. He seems to have chosen the throne over Camilla either volitionally or by default. Many unforeseen events and decades later, he is in position to have both.