What annoys me most about male actors using prosthetics is not that female actors for decades have been expected to do nudity yet male actors get away with showing nothing or faking it, it's not that the prosthetics are so comically bad looking that it completely takes me out of the show/movie, what really annoys me is that so many people are fooled by it and for years we must endure constant reposts and sharing of the same fake nudity from people who believe it's real and will fight with people over its legitimacy.
If they can not make a realistic fake penis, and the actor doesn't want to show his real dick, then they should just show nothing.
I think you are doing a very superficial analysis.
There are many films where male actors show their penis, especially in independent cinema, and even more so in European cinema.
However, every man knows that there are many types of penises, and most penises are different in the flaccid way and erect way. Basically the things about "grower" or "shower". PS mostly are "grower".
The objective of the scene in White Lotus, where Theo appears naked showing his penis, is to generate a specific idea about his character, not about the actor, who needs to show a long penis in a flaccid state to generate the "desired reaction". Most men do not have a large flaccid penis, and Theo is probably one of them. Finally, it is understandable that they use a fake one, since their character must express a "sexual animal" burden.
Now, regarding female nudes, let's say that there are not many films where the vulva of the actresses is focused, only the naked pubes are shown. The equivalent of the male penis is the vulva/vagina with its lips and everything that entails, not the pubis.