Because they're ruthless and proud.
Same reason they keep trying to score as many goals as possible when they are already 4 goals up.
I think they did care enough to:
1) win
2) at least not get humiliated with a 6-0 thumping.
Iniesta in his prime won Euros in 2008 and 2012. And World Cup in 2010. And CL in 2009 and 2011. As well as a Sextuple in there, and Ligas along the way.
So he is the GOAT.
I don't see anything in him either.
At least he didn't cost an arm and a leg, and has very little pressure on him. He can either improve or we can sell him later at not too much of a loss.