Term to describe someone's lack of interest in festive activities
Perhaps you are ascetic?
Ascetic: a person who leads an austerely simple life, especially one who abstains from the normal pleasures of life or denies himself or herself material satisfaction - Dictionary.com
Ascetic: One who is extremely rigorous in the practice of self-denial, whether by seclusion or by abstinence from creature comforts. - OED.com