Comment by crazygringo

It's not that mumbling is in vogue, it's that TV really has become far more naturalistic. We expect people to be seemingly acting like actual people.

When you throw in overly enunciated dialog, the kind you had in 1970's TV and 1990's sitcoms, it's jarring and bizarre. You're like, why is that cop talking like they're in a bad comedy TV show, instead of just being a regular cop? It's seriously terrible.

You still get a milder version of over-enunciation in network comedies today. But it just doesn't fit in dramas that depend on the characters seeming like real people. It's not mumbling and it's not lazy actors, it's a very conscious choice to not distract the audience.