I think it's important to differentiate between very larger-antlered mature bucks and small-antlered mature bucks. Small-antlered mature bucks may die of old age simply because their antlers didn't interest picky hunters. That buck may have learned nothing during his lifetime about avoiding hunters, because hunters didn't want him! He may have walked right by numerous hunters over his lifetime but learned no valuable lessons about survival in a hunted environment. Large-antlered mature bucks, different story...
Deer, just like people, have different personalities. This is genetic. Who with pets hasn't seen this? One pet is as gregarious as all get out, constantly wanting to be at your side, while another is so jumpy and skittish you would swear they don't even live in your house. Some bucks are born ultra-cautious. Some are not. The cautious has a distinct survival advantage, just by luck of genetics.
Although deer probably can't reason (it takes an imagination to reason, and researchers have found no evidence any animal species on the planet has an imagination, with the exception of humans), the certainly can learn through trial-and-error. And once they have learned a survival technique that works, they will keep using the same trick until it doesn't work. Then they will try something else. In addition, as others pointed out, habitat and terrain play a role. Bucks in farmland, being shot from 300 yards away, have little opportunity to learn they are being hunted. However, bucks in thick and/or steep terrain, where shooting distances are very limited, have many more opportunities to get close enough to a hunter to detect them and try a way around them. If it works, they keep doing that.
And of course, the biggy is hunting pressure. The more pressure, the more they learn. I've seen example after example of this. I've worked on properties where bucks are not legal for harvest until they are mature. On very large properties practicing this type of harvest, I've never seen such dumb 3 1/2 year-olds! They have never truly been hunted. They encounter hunters and nothing bad happens. They learn nothing. This leads to some fairly dumb 4 1/2 year-olds!