Why do American sports use playoffs instead of just a league table?

Because the two systems are answering different questions, and each reflects the structure of the leagues that use them.

A league table crowns the most consistent team across a full season. Every team plays every other, home and away, and the champion is whoever accumulates most points. It is the fairest measure of sustained quality, and it is the norm in European football.

A playoff crowns the team that wins when it matters, in a knockout or series format after the regular season.

Why North American leagues favour playoffs:

Closed leagues with no relegation. Without promotion and relegation, the bottom half of a table has nothing to play for from midseason onward. Playoffs keep far more teams in contention far later, which sustains attendance and broadcast value across the whole league.

Geography and unbalanced schedules. Leagues are divided into conferences and divisions, and teams do not all play the same opponents equally. That makes a single table a genuinely unfair comparison, so a postseason resolves it on the field.

Commercial value. A high-stakes single event — the Super Bowl — is worth enormously more in broadcast terms than a title decided by arithmetic in April.

Deliberate competitive balance. Combined with drafts and salary caps, playoffs are part of a philosophy that parity produces better business than dynasty.

The trade-off: playoffs measurably increase the role of chance. The best regular-season team frequently does not win, and in a short series or single game the gap between two good teams is easily swamped by variance. Whether that is a flaw or the appeal depends on your view.

The systems are converging. European competitions have added group stages and knockouts, several leagues use playoffs for promotion, and some North American leagues have added play-in rounds.