honestly I have two theories for why the author decided a new season. First they wanted to create a story but didn't want to go through publishing a whole new work so they decided to create a story mini arc with CBAW, the whole not wanting to publish is pretty common for authors but its usually for side couples
And my conspiracy theory is that BL manhwa has been blowing up like crazy so the author may have created a new season just to bring CBAW back to the spotlight while earning a bit of extra money.
Otherwise I just cant think of why an author would decide to retcon the developments of their characters and renegade the story's ending like this
Clearly it's to make some money; you see the characters acting in ways they would never act with each other after everything they've been through. She just invalidated everything.
"Sighs fine... I made you this way. It's my fault not yours."