Interesting point Pryde, if you like what you do and it makes a liveable income then it can be a joyful activity.
Some people work in jobs they hate just to survive.
The Robin works hard to survive because it knows no alternative.
I think that's the difference?
Many animals survive much longer in captivity as they have no predators.
Other animals die quickly in captivity for a number of reasons. Hence the poem. A metaphor for freedom.
Birds should be free to fly.
I agree. Seems cruel to put an animal that can fly in a cage.