You're right that their lives may not have been that bad compared to being in nature, but in the end, they probably should not have existed in the first place. They were not meant to be in nature from the start. They were meant as temporary living toys, for profit. At least they were not stuck in a key chain or something like that.

Seeing how one would probably not have survived in nature, it's probably best he ended up with me. But the one that died this spring was fierce, energetic and inquisitive. Frankly, she was a jerk and I could picture her being "happier" chasing fish in a lake rather than pellets in a small tank.

Maybe it's a very human and pretentious judgment to make for them, but I can't help but try to put myself in the place of another living thing. You can live safely in a small container with unlimited protein cakes but nothing else to do for all of your life, or you can go explore the world to your own risk and excitement. I know what I'd choose, for my physical and mental health. And I know some animals can get bored and depressed, but I'm not a turtle.