That's a good point, for sure. But on the other hand, some upgrades may be delayed or left undone because more services depend on the same library, so the risk

That's a good point, for sure. But on the other hand, some upgrades may be delayed or left undone because more services depend on the same library, so the risk of breakage is higher. So, there's at least some incentive to using more recent versions, because there's less surface area to test. Not sure how much this affects what's in the wild, though - I mean, I have no data to show that people really do tend to upgrade more often while containerized than not.