I'm aware of why East Germany is more susceptible to extremist voices but I just wonder why they're running to the right instead of the left.
To some extend, they did. PDS and later Die Linke always had their strongholds in the east. The results weren't as good as many would have liked, Die Linke was also torn apart by constant internal infighting and ideological dispute, plus mainstream media being generally antagonistic to them, so I guess now many want to try the other extreme. Also, PDS and Die Linke were never authoritative, and ironically enough plenty of people were actually looking back with rose-tinted glasses to a party who told them what to do, defined everything and offered an easy worldview where people did not have to think, just follow the party line.
But people also went to the far right from the start. The former GDR was also the region where NPD and other far right parties got their best results. I grew up in the former GDR, being born in '85. There was always a strong xenophobic undercurrent, ironically mostly because we had very few foreigners. People of African descent were an extreme rarity, Mediterranean or Arabic people basically completely absent. The only ones with some presence were vietnamese, and they kept mostly to themselves. A few restaurants, little junk shops with counterfeit plastic trash that hardly anyone ever shopped in... they were widely out of the public eye. I remember that my mother and many others tended to derisively call them "Fijis" for some reason - always seemed weird to me, but then again I recognized very early that my mother was a Grade-A moron. People weren't used to seeing foreigners. So when the Wall fell and things went tits up, tons of jobs being lost, drastically rising unemployment rates in states which basically had full employment until then, and the dream of freedom and prosperity quickly rotted... the "Wessis" (west Germans) who "plundered the GDR economy for all it was worth and then left them to rot", as was the narrative. The foreigners were an easy target to blame for competition for the jobs that were still there.
As for the established parties of SPD and Union, to some extend Greens too... well, the east lived under their rule for those past 35 years, and they felt ignored, exploited and looked down on. They'll trust any populist shitebag like BSW or AfD over them, simply because they are not them. And they offer easy populist bullshit, the world does not seem as complicated under them. They don't offer complicated explanations and tough plans, just buy cheap Russian resources for cheap fuel and heating, close all borders so foreigners cannot steal all the jobs while somehow simultaneously exploiting the social systems and bringing in all that crime, and then all is well in the world.