Originally Posted by WareKurt
But what their reasons can be? In Marty2 and Marty3's POVs, everything is normal. There's no way for them to know if anything is changed, unless a third party informs them. Or perhaps Marty1 met them somehow, but Marty3 said "we meet at last" didn't he? I think it is the first time he is seeing the other two.
Marty2 and Marty3 may have had other reasons to make their jumps back.
The three Marty's are a somewhat different case from TP Marty and LP Marty...in that case, LP Marty makes the same trip back as TP Marty did and so the two 'merge' in a sense (as in, LP Marty is erased and replaced by TP Marty, who will later gain the erased LP Marty's memories)...whereas, with the 3 Marty's, they've each made seperate trips.
Let's look at it this way...suppose Marty2 remembered being visited by Marty1 as a teenager...Marty1 asked him to do something which resulted in his current timeline; but Marty2 isn't satisfied with how his life has turned out thanks to Marty1's interference...so he decides to go back in time to just after he remembers meeting Marty1 as a teenager...to warn his past self against Marty1...
So he goes back and does so...now, because of the presence of two future versions of himself, 'our' Marty has a different future from both of them...he becomes Marty3. But for some reason, even he is unhappy with how his life has turned out and blames Marty1 and Marty2 for messing up his life when he was a teenager...so he goes back to just shortly after he remembers them showing up...which leads to the end of the game.