Because rihanna's sound matched her image (good girl gone bad, badgalriri) just like beyonce's sound matched her image (wife, country, classy, diva, sweet, ). They had their own sounds. It was very distinctive/noticable. Writers/producers wrote songs for them based off of their sound they already had and images all of the time. Do your reasearch.
Ego is not rauchy. "turn my cherry out" "on my knees" is raunchy. Rihanna's loud era was rauchy and after that was as well, all of that happened before beyonce's last album. Rihanna's good girl gone bad came out way before beyonce's i am sasha fierce album. Video phone and diva sound nothing like cake and cockiness which are "twerking" or "turn up" songs.
Anti sounds nothing like bryson tiller. Anti is alternative, adult contemporary, and r&b type of music. Lots of different genres. You must not have listened. Bryson tiller is a knock off drake from during his take care sing song days, but more r&b "soul".
Don't play dumb.