Some films and series exist because someone calculated what could be sold alongside them. The reasoning is unglamorous and it explains a great deal about which properties are continued.
Licensing is steadier than ticket revenue
Box office is concentrated into a few weeks and depends on factors nobody controls, including weather and what else opened that month.
Licensing revenue arrives over years, through agreements with manufacturers who pay for the right to use characters on products.
Steady income against an unpredictable one is a meaningful difference to a company planning several years ahead, and it changes which projects survive a budget meeting.
Not every property can be merchandised
Products need distinctive silhouettes, repeatable designs and characters who can appear on packaging without needing explanation.
A story built on adult relationships or on a single location offers a manufacturer almost nothing, however well it performs.
That absence does not stop such projects being made, but it removes an argument in their favour that competing projects can make.
Creature and vehicle designs are the clearest example, since both convert into physical objects with no adaptation and read well at small scale.
The audience for the product is not the audience for the story
Toy lines are aimed at children, and children's purchasing is mediated by adults who recognise the character.
This produces a familiar mismatch, where a work intended for older viewers generates products for younger ones because that is where the licensing market sits.
It also creates pressure on the work itself to include characters and vehicles that will function as products, which writers frequently describe.
Lead times force early decisions
Manufacturing and distributing a product line takes many months, so designs must be finalised long before a film is finished.
Licensees therefore receive character designs early and commit against them, which locks those designs in place.
It also creates a familiar problem, where products reveal a character or a vehicle before the film does, because the retail schedule was set independently.
Why some series continue past their audience
A property with a functioning product line has a revenue stream that does not depend on the next instalment performing well.
That stream justifies continuing to produce material, because the material keeps the brand present and the products moving.
The visible result is a franchise that appears to persist without demand, when in fact the demand is real and is being measured somewhere other than at the box office.