Why did the athenians stay within their walled city during the peloponnesian wars

The Peloponnesian wars fough between Sparta and Athens in ancient Greece, finished around 2400 BCE, with the siege of Athens. The reason for this siege was that the Athenian power had been undermined by different losses, including that of the battle of Aegospotami, in which their fleet, composed by around 180 vessels, was reduced to 10.

Sparta was under siege. Starvation led to diplomacy, and finally, after a few failed attempts an agreement was reached with Sparta which was rather beneficial to Athens, and this was the conclusion of the Peloponnesian War.