Windows is writing to the physical end of my disk

I have a secondary hard drive that I keep all my games and non important data on. I am constantly saving and deleting items off of this drive. Lately I noticed performance degradation on the drive, similar to when a drive is physically full. I took a look at the drive since it wasn't even 50% full and found something like this.

It was actually a lot worse before but I defragged my drive and this fixed the problem. Now that the issue is coming again I checked again and saw the same thing. I always thought real time defrag from products like Diskeeper were a gimmick but is that something I need right now? Or is there another issue?

I have another drive that does not behave like this.

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