Why do some men ejaculate with anal stimulation, but not with having regular sex with women?

Because of the pressure on the prostate gland through anal stimulation the same way a deceased guy male can have his prostate electronically stimulated to harvest semen

Thanks for your response! I am focused on mastering the subject of the prostate! However, because I am a female who lacks the experiences of a prostate- I must go by other people's experiences. All info from as many sources as possible would be helpful..