I don't get it, why should this be folded?

Once again, this is a marginal push. ICM is just a mathematical model and it assumes that others play according to icm too. I bet that 99% of low-mid stakes ICM players would push here.
I think such situations only account for about 1% of ICM decisions so I wouldn't bother about them until you go up the limits.
Probably the trick here is that if BB calls and loses he will still stay in group 2 (stackwise) and you'll still be the bottom group, i.e. you'll have 3k and BB will have 4k, so he could still bully you when you're BB. However, if BB wins, he'll be even with chipleader.
This is an easy and standard push (for me that is ♠_confused: ), ICM doesn't factor in the loss of FE if you fold this hand.
If you fold it, next game you have to push any two, or im wrong? This is total push for me....4bb, next game you are on BB....i would have pushed long time ago and newer got in this mess, but if you are unlucky on cards i can this imagine...
i wouldn't even look at the hand and push here, if you want to win it you have to risk it