Emmy producers are now explaining that while Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matt LeBlanc and David Schwimmer all bagged an invite, they opted not to come together onstage ... cause it was just too soon after Matthew's sudden death in October.

Emmy's EP Jesse Collins tells The Hollywood Reporter he totally gets it from their POV -- they're mourning someone they were very close to for years.

He says while they can't speak on their behalf, they must respect that the "Friends" cast was their own little family.

Matthew was the last person to appear on screen during the Emmys' in memoriam segment honoring fallen stars .... with singer Charlie Puth transitioning from "See You Again" to a stripped-back version of the "Friends" theme song, "I'll Be There for You."

TMZ broke the story ... Matthew was found unresponsive in his jacuzzi on Oct. 28 after playing 2 hours of pickleball at Riviera Country Club near his home in Pacific Palisades. First responders rushed to the property on a cardiac arrest call, and he was declared deceased on the scene after an apparent drowning.

The L.A. County Medical Examiner's Office released the toxicology report in December ... he died from "the acute effects of ketamine," a drug used to treat depression and is also used as a recreational drug.