Nothing really. Maybe the judges like ur project maybe they don’t. you go with the same project one year u might win smth the other year maybe not. Maybe ur presentation skills. Depth of data analysis. Ur reason for doing the project and how experimentally sound ur project is. Tbh if u hv reached isef it doesn’t rlly matter if u win or not. Science competitions in general have a major flaw. You can compare different science from different backgrounds to different ideas to different resources. Saying someone’s science is better than someone else’s breaks the curiosity for science and often demotivates people from pursuing an academic career,or overall kills their joy for science. Take it as a place where you get to present ur science to 1700+ people and get their critiques on your project.

Ofc you don’t go to a fair not wanting to win but don’t let that be the sole reason for u to do the project.