Abortionists are "allowed to stay in the church" because nobody on earth has the authority to remove another person from the church, not even the pope.
However, anyone who commits an abortion or aids in the commission of an abortion is automatically excommunicated, so while they may "stay in the church," they are prohibited from receiving the sacraments until they repent.
By contrast, the most notorious abortionist in the United States, George Tiller "The Killer" is a full-fledged member in good standing of, and a regular communicant at, Reformation Lutheran Church (ELCA) in Wichita, Kansas. Do with that what you will.
I don’t recall that church saying abortion is a sin. They are already reprobates.
And that’s thw rub. Catholics that support or commit abortions still are accepted in to the church anf take the scaraments., and the leaders only move their lips.