Parents and grand-parents who give their daughters princess dresses for christmas and act gleefully if the daughter wear it, express a bias.
Shocking that parents are happy when their daughters like feminine things. It's almost like they don't think they're defective males and their views on clothing is orthogonal to computer issues.
You got it reversely. At first, it's the parents and the grand parents and other relatives who gives princess clothes as presents and then act gleefully. Only after that positive reaction, girls show interest in being a princess, and then parents and grand parents give new girlish presents and again show happiness if the girl smiles. Don't underestimate the amount of impression you make on a child until it conciously expresses interest in some thing and disdain for others! Each toy shop with "girl aisles" and "boy aisles" enforces the gender disparities. Each clothing shop with pink clothing for girls and blue clothing for boys enforces the disparities again. You radiate a message to the child with your bias, which behaviour you consider normal and acceptable and which one you would rather classify as non-typical.
I've seen it unravelling with my daughter. At first she showed interest in the stuff her older brother played with, and in the neighborhood, there were (just by chance) mainly boys. Then a new family moved in with two daughters, and suddenly princesses and horses were all the rage. But when the family left again, the interest in both diminished, princesses were forgotten very soon, horses were of interest until age 9, and now she's mainly interested in computer games, watches countless "lets play" videos, bought a Wii U and a PS4 from the money she begged from the relatives instead of birthday and christmas presents, refuses to wear dresses at all, and in junior high, she took Robotics as optional topic. She likes dystopial novels and movies. And no, she doesn't want to go into STEM, she wants to become a writer for a living (I don't know how this will work out in the end).
People who discount the enormous environmental influences on the choices of young people and who believe in a "natural" interest of boys into STEM and of girls into everything non-STEM seem to be oblivious of the actual situation.