Episodes of the same series can now run from half an hour to well over an hour. The variation exists because the thing that used to enforce uniformity has been removed.
Broadcast length was a commercial specification
A programme filled a slot, and the slot contained advertising. The content duration was whatever remained after the breaks were subtracted.
That number was fixed and non-negotiable, because the next programme started at a published time and the advertising had been sold.
Editors cut to the frame against that target. Length was a specification handed to production, not an outcome of it, and material was removed until the episode fitted whether or not that improved it.
The structure was built around the breaks
Acts were written to end on a moment that would hold a viewer through the advertising. The rhythm of broadcast drama is a direct product of where those breaks fell.
Removing the breaks removes those beats, and the shape they produced no longer has a reason to exist.
What replaced it is not another structure but the absence of one, with length determined by the material. Some writers have built new act patterns deliberately; many have simply let the story run until it stops.
Nothing follows an episode any more
On a schedule, an overrun collided with the next programme. On a service, the next thing is the next episode of the same series.
There is no external cost to running long, so the constraint disappears from the room entirely.
Editors report this as freedom and also as difficulty, because a target length is a useful discipline and its absence removes a reason to cut.
The downstream costs are real
Music licensing, dubbing, subtitling and quality control are all priced against duration. Longer episodes cost more in every one of those processes.
Uneven lengths also complicate scheduling for services that later sell the show to broadcasters, who still need fixed slots.
Some commissioners have reintroduced target ranges for exactly these reasons, which is a partial return to the old constraint through a different door.
What viewers experience
An unpredictable running time makes it harder to decide whether to start an episode, since the commitment is unknown until it begins.
It also removes a useful signal. A viewer used to know from the slot what kind of thing they were about to watch.
Services have responded by displaying durations more prominently, which restores the information while leaving the underlying variability in place. That is a reasonable compromise, though it puts the burden of planning an evening back on the viewer.