Possibly surrounded by a larger place those guys are hunting, guys with money to burn, and locking up that 40 acres ensures some yahoo's aren't coming in and shooting their deer from the bigger surrounding property they manage diligently?
We used to hunt 100 acres from a friend of my dads from work that was completely surrounded by a big commercially hunted ranch. It wasn't 'deer country' per se, but they raised some big deer on that place, and we got some opportunities on their deer that crossed onto our place. It wasn't a big property, but it was close, cheap, and we bow hunted so size wasn't as big of an issue, and we had free rein to do what we wanted year round.
If I had a large spread surrounding a small property and I had spent a ton of money and effort raising a good deer herd, I wouldn't want the little neighboring property to shoot my deer. And paying $10k for the peace of mind may be more economical and neighborly than wrapping their place in a game fence. My FIL has a place innGeorge West, low fence, and 170" and 180" deer killed every year. Next door there was a small cow pasture property. The guy was day leasing it and they were definitely shooting his deer that crossed the fence, so he want and had a fame fence put up just inside his property line down the adjoining part of those properties. Probably a helluva lot more cost than $10k over 5 years