Viewers would plainly prefer one application containing everything, and services keep declining to provide it. The reluctance comes from three things a service loses the moment it sits inside somebody else's storefront.
The billing relationship is the asset
A service that bills a customer directly knows the payment method, the renewal date and the cancellation behaviour. Selling through an aggregator hands all of that to the intermediary.
It also means the aggregator, not the service, decides when to offer a discount, when to bundle and how easily a customer can cancel.
Once the intermediary owns the relationship, the service becomes a supplier to it, which is a structurally weaker position than being the seller.
Viewing data drives commissioning
Detailed viewing behaviour tells a service what to renew, what to buy and what to promote. That information is generated by the player, and the player belongs to whoever built the app.
Aggregators typically return summary reporting rather than raw session data, which is enough to pay royalties and not enough to run a commissioning strategy.
A service without its own telemetry is making expensive content decisions on someone else's summaries, which is why the data argument usually outweighs the convenience one.
Presentation is where subscriptions are retained
The home screen decides what a returning viewer sees first, and that placement is the main tool a service has for surfacing the titles it needs watched.
Inside an aggregator, the service's catalogue is merged into a shared interface where placement is controlled by another company's priorities.
A show the service is trying to build cannot be pushed there, so the marketing spend behind it loses its most efficient channel.
Aggregation still happens, at a price
Services do sell through platform storefronts and bundles, and they accept a revenue share and reduced data in exchange for reach they cannot otherwise buy.
The decision is usually made per market. A service with weak brand recognition in a country will take the aggregation deal there while refusing it at home.
That is why the same service can be a standalone app in one territory and a channel inside a larger platform in another.
What viewers actually get instead
Universal search across services partly solves the discovery problem without solving the billing one, which is why platforms invest in it and services tolerate it.
Bundles solve the payment problem for a fixed group of services and leave the interfaces separate, so the viewer still moves between applications to watch.
Neither approach reunifies the experience, because the fragmentation exists to protect the parts of the business that unification would dissolve.