Where do you get that statistic? You were given a second chance. Tons of people who commit infidelity get second chances for various reasons. The problem is it is a very personal betrayal that pushes a lot of people emotionally. This has nothing to do with men specifically, only that they don’t want to see him hurt. You don’t either, right? So you are really on the same side.
Past experience. Past knowledge. The more often than not correct belief that people don’t really change. If the norm is that a cheater is always a cheater, and you see a friend who was hurt by a cheater get back with them, it is only natural to warn that friend.
Simple as that really. I wish you luck getting through it, but if you truly feel there is no chance of a repeat performance and your bf believes you, why care about well intentioned warnings?
You seem deeply affected by them caring now and not before. Are you worried they will convince him? If not then they will eventually see it worked itself out and stop caring. If not, well they aren’t involved in your relationship so what do they matter? Not everybody will like you, it’s wasted energy to try and make that the goal.