Despite being good value as a cliche, in my 27 coaching career (admittedly not at A League level) I've never actually seen 'caring enough' win that many matches, or prevent that many defeats.
I have, in my playing career. I've played on too many teams where the players thought they'd done their job just by turning up, who were not only not interested in making any real effort on the field, but in some cases thought it was actually funnier not to make an effort (because we're all going to go and have a beer afterwards anyway, which is what it's all about, right?) I've been in teams where the culture actively militated against players who were making an effort/taking it seriously, as being show-offs who were making everyone else look bad.
You wouldn't expect to see that at professional level but that's what I am seeing, and it's my preferred explanation for "Phoenix Syndrome". Why did Bonevacia's performance degrade? What is happening to Rossi? My answer is "dragged down to the existing level". It may be an optical illusion, but I'm not hearing arguments against it at the moment, just people telling me I'm dumb and wrong and should go away because I'm seeing it.