Many men play female roles (maids, mothers, sisters, etc.) in various movies, youtube videos, but they do it with their own free will; no one forces them. Now just think, what if someone forces them to change themselves into females? Sadly this is a real thing. It is called Forced Feminization, where submissive men are forced to change their gender roles, i.e., act and dress like women. This phenomenon is also known as sissification, and these can go to an extent where the submissive male goes through a gender change operation. These submissive males mostly take on feminine roles, roles that are dominated by females like maids, nurses, and teachers. You may notice that females are a majority in the above-mentioned jobs/roles.
Please do not mix this with Transfemme. It's a totally different concept. It means that someone was born as a male, but they do not accept this fact; instead, they prefer to look and act like a female. That specific person may go through a gender change surgery. These people are also referred as Transgenders. read more at transfemme.com
The question now arises from where this change of gender role thing came into existence. A common guess would lead that it might be some dominant women's fantasy, and yeah, it's quite like that. As per the online posts, the women clients of sex workers really loved to dominate them and make them dress as maids or make them do roles that are usually performed by women. The Internet also says that it comes from social/societal pressure. Men are strong, egoistic, and masculine. If the man is forced to do something, he may feel guilty for it, which may act as a vent for his feelings. Some people also do this to explore their sexuality, i.e., to discover whether they are bisexual, transgender, pansexual, etc.
It is pretty common in Japanese and Chinese anime. Moreover, it is now considered a sub-branch of BDSM, where a dominant woman controls the submissive male. read more at https://www.elitedaily.com/p/what-is-bdsm-a-sex-expert-reveals-exactly-what-it-means-8068256
The conversion itself is divided into three categories. In the first category, Sissy Training, the dominant women train the men to be like women in this training. In short, they are trained to be ultra-feminine. The other category is sissy maid training. To explain it in a simple way, just consider that the male does all the house chores while being dressed as a maid while the dominant women just bosses around. At last but not least comes the "slut training". In this, the male is forced to wear revealing clothing, reveal their body. The main purpose of the whole training is to increase the submissive male's confidence and make him proactive, and if he performs a good job, he's rewarded with the deed.
The reason why it is found in movie scenes is to prove that Women, too, are powerful, and they deserve to be considered equals to men in every single aspect. It is usually found in movies where there a majority of popular female actresses.