I'm sure Palestine played a big role in this
I actually don't think so. Die Linke has at best a both-sidesy position on Israel-Palestine. My impression from the people i've talked to is that they don't really think much about foreign policy. It's the progressive economic and social policies of Die Linke that attract younger people. Just like it's not the AfD's stance on Russia or anything as intellectually complex as NATO-EU that attracts people to vote for them, but rather simple things like xenophobia and anti-vax conspiracy theories.
People are primarily worried about the things that personally impact them (or that they think impact them) most immediately. Of course exceptions exist (all of us communists are proof of that), but most people are not as engaged with what is happening in the rest of the world as we are.