What is the reason ? They didn't pay income taxes or what ?

https://www.treasury.gov/auctions/treasury/rp/realprop.shtml

https://howardlevyirslawyer.com/2014/10/19/irs-house-seizure-and-sale-its-less-likely-than-you-think/#:~:text=Losing%20your%20house%20to%20the,unpaid%20taxes%2C%20not%20the%20IRS.