because Volk is a point fighter and he struggled in the 1st fight vs Volk. if he beats Topuria, he's a different beast all together. he's imminently more dangerous than Volk and that was proven when he destroyed Volk and became the first person to KO Max.
he will definitely get credit for beating a fully prepared, full camp Topuria. it'll even raise his stock if he completely destroys Topuria. not only is he a more dangerous fighter, he's undefeated.
i personally think Islam can completely dominate Topuria if he plays his game correctly. i think it's also good for Islam because many of his defenses have asterisks because of the circumstances that were obviously out of his control, but asterisks nonetheless. putting a stamp on Topuria who is as ready as he'll ever be is a big feather in the cap, especially since he'll take his 0 too.
you have to look at it from a casual's perspective, because that is who pushes the popular narrative. we know Volk is a great MMA fighter, but to casuals he looks like a little guy who jabs to win. Topuria on the other hand, even a moron can see he's brutalizing people, some that have never been brutalized like that before. for the casual Volk looks like a nobody and Topuria looks like an animal. you can see this happen with Conor, the casuals thought he was unbeatable, meanwhile most hardcores knew his gas tank and his grappling were sus.