Is it possible that men get testicular cancer for not ejaculating enough?

No: Sperms are made in your testes, but are stored with fluid further on down the line. The fluid comes from prostate and seminal vesicles. Frequency of ejaculation does not seem to be a risk for prostate cancer, though historically men who have had conflicts over this side of their life and tried not to ejaculate under any circumstances have developed precocious prostate hyperplasia.