What I meant was that I think if in Joel's case they had given him decent storylines and a decent amount of screentime he may have stayed. Obviously I can't say for sure, as...well, I'm not Joel so I don't know what the decision was, and it may have been that he wanted to move on anyway, and, yes, it may also have been that he was pushed. But when you have a character constantly shoved to one side and then the actor quits it's not a huge leap of logic to connect the two.
And in Louisa's case, if they'd given half a second to actually think about the character of Ruby and decide which direction to take in her next, based on her personality and who she is, not on what 'explosive' "Johnny returns" plots they can wrangle out of her, then they wouldn't be in a position of "Oh, what can you do with someone who owns half the Square."