The apostle Paul, especially in Hebrews, taught ABOUT the Circumcision gospel, but this is much different than TEACHING the Circumcision gospel. 
He encouraged his brethren according to flesh to hold fast to their calling. But again, this is different than committing himself to overstepping his bounds and moving in on Peter's ministry.

Peter was the minister to the Circumcision, and Paul was the minister to the Uncircumcision (Galatians 2:7). Peter may well have encouraged Paul's people, and Paul Peter's, but they heralded each in accord with what the Lord gave them.

Secondly, it is supposed by some that although Paul calls himself an apostle to the nation, these "of the nations" were still in fact Jews. This is an attempt, I believe, to artificially delay the start of Paul's ministry. For what purpose? Perhaps to prop up the Acts 28 position, which states that Paul did not become the minister to the nations until he was an old man in prison. Now, why would anyone wish to adhere to THIS? Because it relegates Paul's early, pre-prison epistles to Israel. Explaining further, it does away with the snatching away for the body of Christ.

And why would anyone want to dispense with such a glorious event? Well, if one is fairly comfortable, for whatever reason, in this wicked eon, such would be loathe to be so drastically removed from it—especially those of a family bent. I cannot say with utter certainty that this is the only reason for latching onto the Acts 28 position and its sister teaching, the premillennial kingdom, but I do think it plays a significant part.