Why didnt athenians leave city to fight with spartans?

Greek political culture of the time had no real way to integrate outsiders, especially enemy outsiders into the citizen body of a conquering state. You could enslave a defeated population, or you could take the risks of leaving a quisling government behind in a defeated city and hoping for the best. The population of Attica was too large to enslave or slaughter wholesale, and the Spartans knew that conquering and enslaving most of Messenia was the thing that allowed Sparta to rise in the Greek world…but had also made the Spartan state deeply fragile. Trying to hold down an enslaved Attic population just wasn’t something the Spartans wanted to go through.

I hope it helped! Brainliest would be appreciated! ^-^

which time period is this? or is this story fictional, i'm going to need more info to answer this question