Don't ask questions even Bungie doesn't know the answers to. The wall is like that because when porting the Cosmodrome in D2 Bungie forgot the wall was damaged during Rise of Iron. Though the quarantine question is at least easy enough. By the presence of 'irradiated' enemies we can tell it was sealed under Quarantine after the SIVA Crisis and the Fallen pulled out of Old Russia, with the radiation likely resulting from the decay of SIVA throughout the region. Around 2 years later by the time of Beyond Light this seems to have dissipated. I was going to say a better question might be why the Fallen murdered Master Ives, something that was never followed up on directly, but then it hit me. Zero Hour. These House of Dusk members were also serving Eramis, investigating Old Russia, likely for SIVA to convince the Devil Splicers to join them. This would explain why they'd be irradiated, they're actively delving into affected areas and spending time there searching. They didn't find anything, so they captured and interrogated a Cryptarch to find out what the Vanguard did with any SIVA they might've acquired. Hence how they knew that Outbreak Prime (now Perfected) was still locked in the Cryptarch vault within the old Tower and how they were able to perfectly bypass the security measures. I cannot believe it took me so -blam!- long to draw that connection, but then again I think I've thought about that mission twice over the six years since its release.

Where did the bunkers go from that one season with public events?