Festivals announce a handful of names, then more weeks later, and continue until close to the event. The sequence is driven by contracts and cash flow rather than by showmanship alone.
Not every act is booked when tickets go on sale
Organisers need income early, because deposits to agents, site infrastructure and production costs all have to be paid many months before the gates open.
Booking a complete line-up before selling anything would mean committing the entire budget with no revenue against it, which very few operations have the reserves to carry.
Announcing the strongest confirmed names first allows ticket sales to begin and fund the rest, while the remaining slots are still being negotiated.
Headliners come with restrictions
Major acts commonly sign agreements preventing them from playing another event within a certain distance and a defined period around the date they are booked for.
Those clauses have to be settled before any announcement, and they interact with every other festival negotiating with the same act in the same season.
Announcing early can also strengthen a rival's hand in its own negotiations, so organisers hold names back until the terms are signed rather than merely agreed.
Attention has to be rationed
A single complete announcement produces one moment of coverage, after which the event competes with everything else for months.
Splitting it into several announcements creates repeated occasions for coverage, each of which reaches people who missed the last.
Later waves also serve a different purpose, targeting people who did not respond to the headline names but might respond to a particular smaller act.
The later waves fill specific gaps
Organisers watch which stages and days are selling and adjust remaining bookings toward whatever is underperforming.
A day that is lagging may receive a stronger addition, which is why late announcements are sometimes better than their position suggests.
Smaller acts are also cheaper to book close to the date, since their schedules are less fixed and gaps are worth filling.
The final wave is partly insurance
Acts withdraw for reasons no organiser controls, and holding some capacity in reserve allows a replacement without an obvious hole.
Announcing everything early would make each withdrawal a visible subtraction rather than a quiet substitution.
This is why the last additions often appear only weeks beforehand, and why the published line-up continues changing right up to the event.