Cuz he's better. Voldy was trying to kill him while Alby was just trying to protect himself and Harry. He constantly had to have his attention divided to keep Harry out of harm's way and still was putting in work.
Unless Voldemort has his "Horcruxes so he can't die" or his "only Harry can defeat him" stips in play Dumbledore poops all over him.
Even with those stips Albus could still KO or otherwise incapacitate Riddle long enough for a win
Uhm, Albus had the world's greatest wand and he was the one on his ass. Voldemort was all over him. Harry stayed out of harm's way. Voldemort only left due to the orders showing up. I don't see anyone beating Voldemort straight up in the entire Harry Potter universe outside special unique circumstances.
Harry did not stay out of harm's way. Rewatch the fight and you'll see Harry getting up and walking around like a jackass forcing Dumbledore to "Force Push" him back down. (to be fair I think Harry only walked around once but Dumbledore had to push him back down maybe 3? times)
And Voldy stopped battling Albus well before the Aurors came. He saw the futility in trying to best Dumble and decided to "possess" Harry instead. Once Harry resisted and verbally pwnd Voldy THEN the Aurors came making Voldy tuck tail
Dumbledore knocked him down once iirc. Voldemort changed tactics due to his limited time imo. Dumbledore was losing but it was obviously going to take time. Voldemort was in charge of the fight despite Dumbledore having the most powerful wand in existence.
Dumbledore also had to keep pushing Harry down out of harm's way. Even with that distraction Voldemort couldn't come up with a win and had to target Harry instead. So even distracted Albus held Voldy at bay to the point when Mort became too frustrated to continue. He knew he couldn't win so he attacked someone else.
He pushed him down once while he had Voldemort in a bubble of water. False. Dumbledore told him the orders were on their way. He knew that because he was told that. Voldemort knew his time was short so he went after Harry. Dumbledore with the most powerful wand in existence was on the losing end here. Voldemort is better than him.
Just rewatched the scene and i was wrong about how many times Albus "force pushed" Harry and it was only twice. Once right at the start and once again when he had Voldemort in the bubble.
But if you watch the scene you see that even tho Albus had to be mindful of Harry he still had Voldy completely at his mercy. He held Voldy in the water and Voldy was unable to do squat about it. It was only after Dumbledore pushed Harry down(distraction) that Voldy escaped. Had that distraction not happened Voldy would have probably drowned(or at least passed out since i doubt Albus would have tried to kill Riddle)
Dumbledore holding Vold in the air like a rag doll is much more impressive than Vold knocking Dumbledore over especially since Albus still defended against Vold's attack and got right back up forcing Vold to pout and give up.