It's technically not even the rule, it's just the scorer giving it to them every time regardless.
Win (W)
Definition
A pitcher receives a win when he is the pitcher of record when his team takes the lead for good -- with a couple rare exceptions. First, a starting pitcher must pitch at least five innings (in a traditional game of nine innings or longer) to qualify for the win. If he does not, the official scorer awards the win to the most effective relief pitcher.
https://www.mlb.com/glossary/standard-stats/win
When has that ever happened? LOL