For years the four largest tournaments finished deciding sets in different ways, and some still differ from the events around them. The variation came from a scheduling problem rather than a philosophical disagreement.
Advantage sets have no upper bound
A set requiring a two-game margin can continue indefinitely, because a player holding serve reliably prevents the margin from ever appearing.
On faster surfaces where serve dominates, that produced deciding sets long enough to consume an entire day of scheduling.
An unbounded match is unmanageable for broadcasters, for the tournament's court allocation and for the players who follow on the same court.
Tie-breaks convert an open end into a fixed one
Introducing a tie-break at a set score of six games all caps the length of a set and makes match duration predictable.
Applying it to the deciding set removes the last source of unbounded length, which is why events adopted it for earlier sets long before extending it to the last one.
The resistance concerned tradition: a deciding set played to a margin was seen as the fairer test, since it required a player to actually break serve.
The compromises took different forms
Some events introduced a tie-break only after the deciding set reached a much higher game score, preserving most of the traditional structure while capping the extreme cases.
Others adopted a longer tie-break requiring a wider margin than the standard one, on the basis that a deciding set should be harder to close than an ordinary one.
Each solution reflected a different weighting of tradition against schedule, which is why the four largest events arrived at four different answers.
Standardisation followed player experience
Playing the same tournament under different deciding-set rules from one week to the next affects preparation and tactics in the closing stages.
Pressure to harmonise came largely from players and from the practical difficulty of preparing for inconsistent formats.
The agreed approach settled on a longer tie-break in the deciding set across the major events, keeping length bounded while making the final passage more demanding.
What it changes tactically
Under an advantage set, a returner can accept a long attritional passage because there is unlimited time to break once.
Under a tie-break, points arrive in a short sequence where a single mini-break decides everything, which rewards the server and the player who handles compressed pressure.
The format therefore alters who is favoured at the end of a close match, which is precisely why it took so long to agree.