Turkish Airlines Overbooking Issue on Diyarbakir-Istanbul Flight

I arrived at the airport around 11:20 AM for my Turkish Airlines flight with PNR code scheduled for February 18 at 12:15 PM from Diyarbakir to Istanbul. I got in line at 11:30 AM with only one person ahead of me. The person in front of me completed their transaction, and when it was my turn, I handed over my ID. However, the staff informed me that the check-in period had ended and that check-in could not be done within the last 45 minutes. Yet, the person in front of me had just completed their check-in 30 seconds earlier, and I was waiting in line. Did I really miss my flight by just one minute? I expected the staff to have a high level of work discipline, but this was not the case. Many people who have flown from Diyarbakir Airport have mentioned completing their check-in within the last 30 or even 20 minutes, including myself. While talking to the staff, I learned that there were no empty seats on the plane. However, there were 7-8 people like me who were not allowed on the plane; how could this be possible? I got the impression that Turkish Airlines sells more tickets than the plane's capacity, knowing that passengers might be inconvenienced. The ones who suffered were students like me who needed to get to university classes on time, wasting both time and money. Additionally, while waiting, I overheard a conversation between staff members about allowing a passenger on board if they were in business class. I don't want to blame anyone, but I request that this situation be investigated. It saddens me to think that even in one of Turkey's largest and globally recognized companies, 'money talks' might be the underlying principle. Thank you.