why 'women and children first' and not 'first come, first serve'?

hi, i just read my stepson the magic treehouse book tonight on the titanic and the moment he went back to his mom's i went down a titanic rabbit hole, so forgive me if this is common knowledge but i am so stumped on this.

the titanic famously only allowed women and children to board their lifeboats (besides a few men who either snuck on or were allowed on to row). i used to think this was chivalrous and made a certain kind of sense considering they had limited lifeboats and you would prefer to save children over adults, but i just watched Titanic: Honor & Glory's real time titanic sinking on youtube (i saw the original 10 years ago but did you know they made a really impressive updated one?) and now i am just so confused. i always heard that they didn't fill up some lifeboats to full capacity, but now i see they only filled ONE out of TWENTY lifeboats, and those 19 others were mostly only half filled?

the reasons i have read is that people were initially not convinced the ship was sinking, or they were scared of the lifeboats, or they didn't want to leave their husbands/fathers. they only filled half of the lifeboats because there just weren't a lot of women and children around, but instead of filling the rest of the boats with men they just lowered them into the water, to the extent that they physically tore husbands and wives apart and shot warning shots to 3rd class passengers trying to board?

i think they would have been more prudent and successful in saving more lives if they did a first come, first serve basis and not women and children first. i just recently got married and i keep getting choked up reading survivors witness accounts watching their husbands waving goodbye while they get lowered in half filled lifeboats. i am just so frustrated by all this, can someone who knows more help me understand why they were being so weird and insistent about not saving men or 3rd class passengers?