Can you please specify if low hashrate or a known vulnerability was the problem (or both)? With vulnerability are you merely refering to a more conservative max_reorg figure or do you think there is a more serious problem? If so, why can this be shared with the community or the devs when a problem in code is actualy found?

Space Blockexplorer is and has always been here: http://space.midnightminer.net/ , working fine as I can judge from daily use.
SJW Blockexplorer is since roughly a year here: https://sjw.netcraft.ch/ (this has been brought to Cryptopias attention even, also working fine)
GEN was unlisted because it's self-proclaimed dev Hort had an argument with Adam and it got delisted/deactivated same day (only quote of Horts post available: https://bitcointalk.org/index.php?topic=1205536.msg16038573#msg16038573)

Also I asked Lafu about Space removal in a german thread and only got referred to their coin listing policy in general. leaving unanswered if there is a problem in code they are unable to share info about or just the low hashrate that they saw as a danger for double spends in deposits.