Games are announced with dates and then moved, sometimes repeatedly. The pattern comes from a mismatch between when a date has to be committed and when it can reasonably be known.
The date is set long before it is knowable
Dates are announced to secure marketing slots, retail attention and coverage at industry events, all of which are scheduled far ahead.
At that point a project may still be in a stage where major systems are unfinished and their interactions untested.
The commitment is therefore made on a projection, and projections made from that distance carry a wide margin that is not communicated publicly.
The final stage is the hardest to predict
Building features is comparatively estimable, since the work is understood and progress is visible as things appear.
Making a large interactive system stable is not, because problems emerge from combinations of systems that only become testable once everything is present.
A single issue affecting saved progress or performance on one configuration can consume weeks, and there is no way to know in advance which will appear.
Certification and platform requirements add a fixed tail
Console releases must pass technical certification, and a failure sends the build back for changes and resubmission.
Physical releases add manufacturing and distribution, which imposes a hard cutoff weeks before the date anyone can play.
These steps are not flexible, so any slippage in development is absorbed entirely by the team rather than by the schedule.
Delaying has become the cheaper mistake
Releasing a game in poor condition now produces sustained public criticism that follows the title indefinitely and depresses sales well beyond launch.
A delay produces a short period of disappointment that is largely forgotten once the game arrives and works.
Publishers have adjusted accordingly, which is why late delays have become more common rather than less as the industry has matured.
The calendar constrains where a game can move to
Release windows are crowded, and a title moved by a few weeks may land against a much larger competitor.
Delays are therefore often longer than the work requires, jumping past a busy period to a quieter one several months away.
This is why a game needing an extra month is announced as moving to the following year, which looks disproportionate until the calendar is taken into account.