why is stalemate a thing
1. It's been a rule for a long time, changing it would create quite a lot of confusion
2. The possibility of stalemate has led to some very interesting games, where a player can sacrifice pieces in what would be a losing position without a stalemate, in order to achieve stalemate.
Stalemate is a requirement of the rule that a move by a player can never expose their own king to check. How that impacts the result, has changed over the years.
There have been times where the stalemating player loses the game, the stalemating player wins the game, or the game is a draw. The latter case makes the most sense to me.