I posted this elsewhere before but in 1991, the average length of a game was 2:54. Last year it was 3:04. In the last 25 years the average baseball game has been 3 hours, plus or minus about 8 minutes.
From the 50s through the end of the 70s it was very similar, games were right on 2:30. The big jump in game length came from in the decade and a half from about '77 to '91.
I'm all for shortening the game, I'd love something closer to 2:30, but this isn't a new "problem". Being in my 30s I literally can not recall watching a game that wasn't about 3 hours. If folks think the game is slow or boring now compared to 25 years ago, its probably from changes within the game rather than just the duration.
Or maybe it was the rise of cable networks and the ability to watch literally every single game that's leading to burnout. I dunno.