@minhnimumpoint First of all, I hope you did a manual uninstall before reinstalling. The uninstaller that comes with the game can miss some files, which could later interfere with your current installation.
But to answer your question, it's likely that you had a second TS3 folder hiding somewhere on your computer. These rogue folders can be difficult to track down; the best advice is to start a new save and give it an unusual name, and then search for that name on your hard drive. Now though, your TS3 folder is probably being stored in OneDrive (PC) or iCloud (mac), which is where the second folder could have been before. Both Windows 10 and the latest versions of mac OS just love synching the Documents folder to the cloud and will make every attempt to do so if not stopped. But your game can't find its folder there, so it generates a new one every time you launch.
It's simple to prevent macs from depositing documents into an iCloud drive, but OneDrive is more stubborn. It might be best to disable it entirely, especially if you're not using it for anything else.
If you disable cloud storage and still can't find your folder, you can still go looking for it using the same method as described above. Once you launch the game for the first time on a given computer, a game folder will inevitably be generated, and it has to be there somewhere.
