Bad writing 101: When you know you've written yourself into a corner, simply move the goalpost, no matter how obvious it is that you're doing it.
BoG (anime and partially manga): SSJG Goku gave Beerus a genuine challenge and was not an easy opponent for Beerus to overcome.
RoF (anime): Goku and Vegeta have gotten closer, and when teaming up might have a shot against Beerus.
U6 Tournament (anime): Beerus is concerned about Goku having Super Saiyan Blue Kaioken and Whis questions if Beerus is afraid.
Goku Black Arc (manga): Supreme Kai thinks Vegito is probably > Beerus.
Exhibition Match (manga): Jiren stated to be stronger than Belmod in terms of raw power, who was arguably implied to be on a higher-level among the GoD's.
ToP (anime): Goku and Jiren stated to be above the GoD's numerous times, Goku achieving a state Beerus could not obtain. Goku beating Jiren who was stated to be stronger than his own God of Destruction, who was stated to be stronger than Beerus.
ToP (manga): Implications that Goku and Jiren are probably around Beerus level.
Nearly everything after the ToP: Beerus still shitstomps no-diff kekw.
Fr, Beerus is like >>>>>>>>>>>>>>>>>>Black Frieza apparently, who just casually mutilated and killed Gas, who was in the process of wrecking Goku and Vegeta's shit while dying. Toriyama, Toyotaro, whoever tf is still writing seriously does not want Beerus to be surpassed by anyone who isn't already stronger than him.