I bet they all were cringing, I would have cringed as well if the manager kept rolling out his mates to give boring "United way" sermons.
The only reason you would have to cringe if you were being addressed by someone with lesser accomplishments than you.
However, to a lot of these players, and ESPECIALLY the men who came through the academy, Roy Keane is essentially a deity. He's also one of the most famous and accomplished captains in club history who was there for the most accomplished period under the best club manager in the world. The only person in Manchester United that was there in the 90s and 00s and that carries a remotely similar
gravitas than Roy Keane, is Sir Alex himself and Eric Cantona.
And you assume that the kids are cringing to be given a speech from that man?
You're missing the point about playing on the Theater of Dreams. You need something to motivate you, and what is better than a history lesson from someone who was there for the same period they are trying to achieve as a group?
If I'm being given a chance to listen to someone in my profession who has achieved more than me, I sit down and listen.