Then in this case, I could ask you, What's the difference between the OP's case and a person who has a very long connection, goes on a TK Istanbul tour (and therefore is not entitled to a hotel by TK) during the day and stays at the lounge at night? or do you think in the latter case they should also be banned from the lounge? but I'm not going to ask because I think I already know the answer.

My main point here that I would like to express is that there are regulations in place by TK, and each person can utilize the regulations as they see fit. We don't really know why OP wants to stay at night in the lounge. Maybe it's the first time there; maybe this is an award ticket, and spending extra on a hotel makes things much more expensive; or maybe an old friend will transit at that time in IST.

If you think that the regulations are too permissive, you should reach out to TK and express your discomfort. Some airlines, such as RJ, limit their lounge access to 3 hours before a flight (in the case of non-transit). TK can do the same if they want to.

I'm also not happy with the situation at night in the TK lounge at IST. But I would suggest TK not limit access to the lounge but rectify the situation by providing beds to anyone who requests them. My vision is that a large hall will have replicas of the 777 or A330 J seats (i.e., no electronics and no moving parts) spread out in a 1-2-1-2-1-2-1 configuration to resemble the J cabin. This is a really cheap option (price-wise and real estate-wise) to implement and maintain.