Well, you thought wrong! We didn't have a permanent address when we arrived, we were in a hotel. Many people, especially DV selectees not coming in to stay with family, stay in temporary lodging until they find a place to rent. Why would you think they expect everyone to have arranged permanent accommodation before setting foot in the country?
And you can pay the $220 fee after you arrive, just be aware you don't get sent your plastic green card until you do. The official USCIS page states this quite clearly:
You may also pay the fee after you arrive in the United States. https://www.uscis.gov/file-online/uscis-immigrant-fee
Your endorsed-upon-entry visa turns into a temporary green card for a year after arrival, so you can use that in the meanwhile for anything you need a green card for.
