if you believe in the social construct theory

then there are easily two genders by default

a trans will identify with male or female

genderfluid is just a term that hipster use to say "im very gender neutral"

but they will still nonetheless identify with a certain gender by default

Naturally, but I'm looking more for why people wouldn't believe in that.

ah it's because they are butthurt

This feminism movement has always been a reactionary movement

whatever "patriarchy" does

movement reacts

what is good to the patriarchy is evil to the movement

patriarchy recognize on a good/bad basis

the movement recognize on a good/evil basis

So instead of saying it is bad to make women pay more for female products

IT IS EVIL

that the men's product is priced cheaper than the female's product

it's not like the store are gonna give you weird looks for buying a man's product as a woman

I'm not following how that relates to the question, sorry

The reason that more than two genders exist

is on a reactionary movement

They want to break the concept of two genders because it doesn't fit them

Not that,
I want to know the arguments Why people don't Accept the idea of more than two genders.

that is literally the argument

people don't accept the idea of more than two genders because it is a purely reactionary movement

instead have to spoonfeed it to college students

where they are forced to take 2 diversity classes before graduating

do you think a guy who worked 40 years is going to care if there are more than two genders?

people are still people

so the fact that we're attempting to change this is purely reactionary

If you truly ask people who believe in more than two genders

Then you ask them what's the premise of the argument then?

They will usually say intersex people

XXY, XYY, XXXY.

If XX and XY are the main genders, what happens to these people?

XXY is more feminine yet has a small dick

XYY is very masculine yet for some reason has a defect in testosterone(idk why)

but yet when u look at them

are they radically different from an XY or XX?

So why do we have to make a separate gender?

If the 2nd premise is gender is a social construct

"it's what you identify as"