Festival lineups are typically revealed across several announcements over months. The staging is partly a marketing decision and partly a consequence of when contracts are actually signed.
Bookings do not close simultaneously
Headline acts are secured first because everything else is arranged around them, and those negotiations can take months to conclude.
Smaller acts are booked later, often once routing is settled, since a band will accept a festival date that fits an existing tour and decline one that does not.
A festival that waited to announce everything at once would be holding confirmed acts back for months while competitors announced theirs.
Staged announcements extend the promotional period
A single reveal produces one burst of attention that fades within days, while several announcements produce repeated occasions to reach people who were not ready to buy the first time.
Each wave also reaches a different audience, since a smaller act announced later brings its own following into contact with the event.
The order of the waves is chosen deliberately for that reason, with later announcements weighted towards genres or scenes the earlier ones did not serve.
Early sales happen before the lineup exists
Many festivals sell a portion of tickets before announcing anyone, relying on the event's reputation rather than on its bill.
That arrangement is valuable because it provides cash early, which is when deposits for artists and infrastructure are due, long before any revenue would otherwise arrive.
It also reduces the risk that a weak reception to the lineup leaves the event without a base of committed attendees.
Exclusivity clauses shape the timing
Contracts often restrict an artist from performing at competing events within a defined distance and period, and those terms have to be settled before an announcement.
Where two festivals want the same act, the announcement is sometimes delayed until the surrounding arrangements are resolved, which is why expected names occasionally appear late.
Those clauses also affect an artist's own touring, since accepting one can close off headline shows in the same region for months either side of the festival date.
Late changes are built into the process
Acts withdraw for illness, visa problems and scheduling conflicts, and replacements are found close to the event.
Announcing in waves makes those substitutions less conspicuous, since audiences are already accustomed to the bill changing as the date approaches.
Stage times are usually held back until last for the same reason, as they are the element most likely to shift and the hardest to correct once published.