Most early Christians were converts from Judaism so they were doing circumcision as tradition but the Greeks in particular did not like it and that’s where Paul’s ‘don’t worry about it’ letter comes in. After Christianity solidified into its own religion there was a move to break from the religion’s Jewish roots and carrying on practices from the Old Testament were seen as too Jewish- circumcision was the easiest one to check for when you were got paranoid that there were Crypto-Jews hidden among your population.