Why did gulliver want to leave the kingdom of brobdingnag,and how did he manage to reach sea coast?

Gulliver has been in Brobdingnag for two years and strongly feels that it is time to leave. He is basically being treated as a pet. But the royal family does not want to part with him. Coincidentally, on a trip to the seashore, a giant eagle picks up Gulliver's traveling box and flies off with him. Realizing that the box is not edible, the eagle drops it into the sea. After some time the box is picked up by a passing ship of Gulliver's normal proportions