Variance is punished differently
Across a long regular season, an unlucky bounce or two evens out against a large enough sample of games. In a single-elimination format, the same unlucky bounce simply ends the season, with no following week to correct the record. This changes what a smart team should optimise for once the format shifts: not just being good on average, but minimising the chance of a single catastrophic afternoon.
That is part of why conservative, low-variance approaches sometimes appear in the postseason from teams that played more aggressively during the regular season. The incentive structure has genuinely changed, not just the stakes.
Preparation time changes the contest
A regular-season opponent is often prepared for in less than a week, competing for attention with the previous and following games on the schedule. A postseason opponent, particularly in a rematch, can be studied with an intensity that a compressed regular-season week never allows, and that extra preparation tends to narrow the gap between mismatched rosters.
This is one reason upsets cluster in the postseason more than raw talent gaps would predict: a well-prepared, unified game plan against a specific opponent can offset a real difference in overall roster quality more easily than in a normal week.
Built for one format, tested in the other
A roster genuinely built to win a long season — deep, flexible, able to absorb an injury — is not automatically the roster best suited to winning four single-elimination games against increasingly prepared opponents. The two goals overlap heavily but are not identical, and front offices make real trade-offs between them.
Recognising this explains why a team that dominated the regular season sometimes looks unrecognisable in a tight postseason game, and why that is a legitimate structural feature of the format rather than a mystery. Arena's NFL postseason guide explains how the bracket and seeding actually work.