Wolverine's healing factor keeps him alive, but Thanos's cosmic power means Logan can never actually hurt him.
Similar to Deadpool vs. Thanos โ Wolverine cannot die, but also cannot win. Thanos's base durability is so far beyond what adamantium claws can damage that Logan's offense is effectively zero.
Thanos has tanked planet-busting attacks from cosmic beings. Wolverine's claws, while able to cut through virtually any earthly material, face a very different challenge against Eternal/Titan skin that has withstood the Power Cosmic. The best Logan could hope for is superficial cuts.
Meanwhile, Thanos can obliterate Wolverine's body with energy blasts. The healing factor would bring Logan back eventually, but 'eventually' isn't a win condition in a fight.
Thanos's durability likely exceeds what adamantium can cut. His energy projection can vaporize Wolverine repeatedly. His intelligence lets him find permanent solutions if needed โ Thanos has the resources to contain or neutralize healing factors.
Wolverine cannot be permanently killed. His adamantium claws theoretically cut through anything. His berserker rage makes him fearless and relentless. Logan has fought cosmic-tier opponents before and survived through sheer refusal to stay down.
Thanos wins decisively. Wolverine's incredible tenacity is admirable but irrelevant against someone who can casually tank planet-busting attacks. Logan survives through his healing factor, but surviving and winning are very different things.
Thanos also fights
Wolverine also fights