This is an often overlooked aspect indeed. I'm amazed at how much people underestimate the impact that being dead has on one's humour.

Delivery becomes impossibly hard. Having a working respiratory system and vocal tract is often expected by the audience, and typical physical humour becomes a stiff challenge.

"Resolving incongruity" is often a key component of humour, but the brain struggles to make sense of something that is out of place when it becomes completely electrically silent.

Gallows humours, hilariously ironic to the living, loses some of its impact when you become the literal subject of the joke.

After dying, our audience is notorious difficult to read, and don't really offer laughter.

More importantly, humour carries a dopamine reward, which is greatly reduced to zero, which further disencentivizes it.

It's rather grim, really.