“These are DC’s characters, we’re just renting them ya know, so we use the characters that they tell us we can use when we can use them, and we work around whatever limitations that places us,” Guggenheim explained.

“For a time they were saying ‘you can’t use Deathstroke’, and that changed and we were able to have Slade Wilson back on the show, and now we’re back to ‘you can’t use him’. They’re working on the feature film version.

batman-news.com/2017/12/21/arrow-cant-use-deathstroke-again/

the stupid thing is that they are worried about "brand confusion" and using the characters on TV will somehow damage the value of the character in potential movies, but the only thing that confuses people is the back-and-forth he's-in/he's-out, especially when they kill a character off just to bring him back again