I live in a rural area with indoor/outdoor cats and I've seen that too, honestly it feels like a pretty classic bathtub curve, or that curve showing experience vs survival whose name I'm spacing on, the one with the dangerous "knowing just enough to be overconfident and kill themselves" valley. Some cats are inherently more cautious, but in general over the decades my observation has been that in general cats are like humans who engage in risky but rewarding behavior be it work (factory, or devops for that matter cough) or sports such as rock climbing or kayaking. When someone (or some cat) is absolutely brand new to the world, nearly everyone is very careful. Then they grow in comfort and experience, having learned a lot of the basic ropes, and in turn get more and more confident. But they haven't had their first crisis yet. Eventually comes the inflection point, where overconfidence leads to some sort of life/death (or losing the production database and holy shit are you fucked) moment with a rare event.

Those cats (or people) who make it through that crisis will gain some hard humility forever more and seem to go on for a long time after. Those who don't, well, obviously that's it. I had two big male cats back in the 90s, who being tough young males naturally once they got to 2-3 years old felt pretty confident. First of them sadly vanished and never saw him again. The second a few years later got into some fight or flight with/from something, I don't know what, but there were shrieks. But he escaped/fought and I found him. Forever after he was very careful, he'd go out the door onto the porch and whereas before he'd just instantly head off, after he'd immediately sit down and observe/listen for a good long while first. He lived to 21 years old. Another outdoor/indoor lived to 19.

It is truly hard to take the risk, but they're so much happier for it. We all reach the same end in the end, so I feel very strongly that there are limits to how far one should take "being safe". And there are good ways to massively reduce the bird issue. I love birds as well, but 3-5 caught per year when I'm feeding and support orders of magnitude more birds than that seems acceptable.