Has to do mostly with the historic environment of the country. Berlin was a split city, so after the 90s it abstained mostly from what it perceived as dangerous political experiments. Also die Linke was basically seen as a continuation party of the GDRs SED, and as such didn't have the greatest of reputations in that city (shooting/jailing people that want to move out will do that miraculously).

Die Linke today is a completely different generation of people and drawing any direct line to the SED is mostly wishful thinking by polemic conservatives.