Why are BL authors so obsessed with giving villains a happy ending by getting them into a ...

I think that there can be 3. Possible reasons
1. The author grew on them
2. Fanservise
3. They are scared they will isekai as villain without happyending

For money LOL. They know people will read it, and even if the story is bad, people are still willing to spend money and support it. For example

https://www.mangago.zone/read-manga/my_suha/

https://www.mangago.zone/read-manga/sadistic_beauty_bl_sidestory/

Definitely 3.

You just made me realize that people spend ACTUAL MONEY to read those kinds of side stories

SMH, for real. I dropped My Suha after about 10 chapters, but sometimes, out of nowhere, I’d check the comment section to see what was going on—and I was thankful I dropped it. ٩(๑❛ᴗ❛๑)۶ I honestly think My Suha has the worst and dumbest side stories. If I had to answer OP, I’d say the creators just lacked the intelligence to end the story strong and ran out of ideas so they tried to turn the villain over a new leaf instead. They should’ve just moved on to their next manhwa.

Yeah, I also think there is a large audience for that who are willing to spend money on it.

Definitely #3 it's also nice to see Redemption, Character Growth, Forgiveness etc. but still Definitely #3

Yeah, I've seen this happen a lot, and I'm tired of it. I don't want to read a side story of a character that was an asshole that raped or SA the MC, WTF! Making the character have character development isn't going to change my mind about them （￣へ￣）

And the character development always feels very sudden and forced

Literally Incorrigible. Why's that shit rated so high the ml doesn't deserve that rapist mc smh. No one does just let him die alone.

So true OMFG! I prefer for a bad character to have no happy ending