Comedies from a few decades ago frequently feel dated in a way that dramas from the same period do not. The difference is structural, and it follows from what a joke actually requires in order to work.
A joke depends on a shared expectation
Most humour works by setting up an expectation and then breaking it, which means the audience must already hold the expectation before the joke begins.
That expectation is supplied by the culture the audience lives in rather than by the work itself, and none of it is stated on screen.
When the assumption fades, the setup no longer registers, and the turn arrives with nothing to push against.
Drama runs on slower material
Dramatic writing draws on grief, ambition, betrayal and love, which are recognisable across long periods and do not require a particular cultural moment.
A drama can therefore survive unfamiliar clothes, technology and social arrangements, because the audience follows the feeling rather than the reference.
Comedy has no equivalent reservoir. Its raw material is what a particular audience currently takes for granted.
Timing conventions shift as well
Pacing is part of the joke, and the rhythm audiences find natural changes measurably from one era to the next.
Older comedy often plays slowly to modern viewers, holding a reaction longer than it needs, and the delay itself dampens the laugh.
This affects performance styles too, since a broad delivery that once read as energetic can now read as strained.
Topical material has a fixed expiry
Jokes about a specific event work brilliantly while the event is current and become inert the moment it is forgotten.
Writers accept this trade knowingly, because topical material lands harder than general material with an audience that recognises it.
The consequence is that the funniest parts of an older comedy are often the ones that were never about anything in particular.
What survives tends to be structural
Comedy built on character, physical construction or the mechanics of a situation lasts longer, because none of those depend on a passing reference.
A misunderstanding that escalates because two people will not admit ignorance is legible to almost any audience at any time.
This is why silent physical comedy remains watchable while verbal comedy from far more recent decades often does not, and why writers aiming for longevity build jokes into situations rather than into lines.