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Why is the prisoner’s dilemma a noncooperative game?

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A colorful payoff matrix for a normal form game in game theory, showing strategy options-support, oppose, evade-for both party A and party B. Each cell contains cartoon figures representing each party's action and lists percentage payoffs for A and B. The bottom-right cell is labeled saddlepoint, highlighting the equilibrium. — game theory Table 1
The normal-form table illustrates the concept of a saddlepoint, or entry, in a payoff matrix at which the expected gain of each participant (row or column) has the highest guaranteed payoff.

The prisoner’s dilemma is classified as a noncooperative game because it lacks a mechanism for players to make and enforce binding agreements. In game theory, a game is considered noncooperative if players cannot enter into enforceable contracts or commitments that guarantee specific outcomes.12

In the prisoner’s dilemma, the two suspects are isolated and cannot communicate to coordinate their actions. Even if they could communicate, they lack an outside authority to ensure that a promise to remain silent is kept. Because there is no way to penalize a player for breaking an agreement or to guarantee that the other party will cooperate, each player is incentivized to act in their own self-interest—which, in this scenario, means confessing to minimize their own prison sentence.342

This leads to a Nash equilibrium where both players confess, even though they would have achieved a better collective outcome by cooperating and remaining silent.42