Masturbation and ejaculation are useless nowadays

Hello Rabbi,
I've heard of studies that claim that ejaculating protects against prostate cancer. I also saw that it says in the Rambam:

And when he ejaculates, he does not ejaculate except to warm his body and to sustain the semen; therefore, he does not ejaculate whenever he desires, but whenever he knows that he needs to ejaculate a layer of semen , such as through the healing process , or to sustain the semen.
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The wise physicians said, one in a thousand dies of other diseases; and the thousand, from excessive use. Therefore, a person must be careful about this matter, if he wants to be in good health. And he will not have a boil except when he finds his body very healthy and strong, and he is having a lot of difficulty without knowing it, and he distracts himself with something else, and the swelling is as it was; and he finds a heaviness from his waist and down and as if the strings of his eggs are being pulled, and his flesh is hot. This is necessary for a boil, and the cure for it is to have a boil .

If so, it seems that according to Maimonides, there is a need to ejaculate. If so, why shouldn't a single man be permitted to ejaculate from time to time (since it's not ejaculating for nothing, but for some purpose)? Similar to what you wrote in this responsa. Especially in our day and age, when there is a phenomenon of late singlehood, and a man can find himself in a situation where ejaculating is prohibited for many years. Furthermore, it is possible that not ejaculating causes more sexual thoughts.
Best regards,