Joking aside, I am surprised how fast invidious and other open source projects run, and how slow runs youtube. Does algorithm need to think about which advert

Joking aside, I am surprised how fast invidious and other open source projects run, and how slow runs youtube. Does algorithm need to think about which advert to put? Is it because JS/CSS is so bloated? Is it because everything corporate runs slower on firefox? Maybe youtube just runs faster on chrome? Dark design?