Particularly, why I was suddenly blacklisted after more than 2 months of inactivity!

You were probably blacklisted a long time ago and just never knew it. It's this new (software) version they just implemented that shows the red (1) next to your name that now makes it into a "scarlet letter".

Marky's pushing for a "grand-unified-master-blacklist" across all the major front-ends.

Details here,
https://steemit.com/sps/@themarkymark/global-blacklist-api-proposal#@themarkymark/q6fmzx