They're aware of the signs of gambling addiction, but still lack self control. A responsible gambler with a plan would recognize when they are losing too much and take steps to prevent addiction, without needing from others. As the saying goes, A good person advises themselves after all self reflection and introspection can be more valuable than advise from others.
You said a responsible gambler will always know, that's correct, but anyone who gets addicted to gambling is never a responsible gambler in the first place.
Those who are not responsible in some cases don't consider what we see as signs of addiction as one; most times they don't even agree to it when you present it to them; they always think they are in control of the whole situation and don't need couching; only those who do realise on their own and will to adjust visibly admit to being addicted.