I think it's not so much the shampoo but a mix of most men using shorter haircuts and doing less damaging things to their hair, like hair colouring.

And it's not like there aren't specialized shampoos targeting primarily men. I think I never saw a dandruff shampoo marketed towards women.

For the pants, it's partly the hip/waist ratio and partly the extra bunchy fabric in the crotch region.

Some already do.

And man pants aren't that big of a hurdle to get used to. Just need to take measurements of waistband and inseam and you've got the size to look for in mens pants. Thats what I like about them: they have much better sizing labels than the nebulous/arbitrary size numbers on women's pants.

Almost everything on the market is shit and will destroy your hair. That includes the 6 in 1 shampoo, men just usually have less hair.

When I was in high school the trend was baggy pants and lots of women did wear men’s pants.

It's nonsense, and men with longer hair who use 6 in 1 have bad results. Longer hair takes more treatment, hair is usually vitalized by oils from the scalp, so the further away from the scalp the more help it needs to stay healthy.