It’s just a way of addressing the hired staff to make sure that everyone recognizes them as hired staff, not lay volunteers. Don’t get so worked up about how others do it. You’re not a member of their churches, so don’t fret about it. It doesn’t affect you. And it doesn’t water down the term “pastor” or diminish it because they have a different understanding of what a pastor is than Catholics.
I’ve been part of Protestant churches where there are no “pastors,” but everyone is called either “Brother” or Sister." I suppose a Catholic could get worked up over that, too, since these people are not consecrated to a religious vocation.
This is an “authority” issue, and you must understand how each denomination designates authority in order to understand why the various “titles” are used. You can’t make a blanket statement about Protestants because these authority issues are different for every denomination. The way to understand the “chain of command” is to ask when you visit that church.
Richard Kastner brought up a very interesting point, that many Protestant denominations organize their church according to the spiritual gifts. “Pastor” is one of the Gifts of the Holy Spirit (according to Ephesians 4), and so that name will be used to address those in the church with that spiritual gift.
In many Protestant churches, the hired staff are often given some form of “address” that is different than everyone else in the church so tha these people will be recognized as hired staff, someone who has a “job description” and who can be called upon to do a task for the church. It’s a way of making sure that these people are viewed in an “authority” role by those who attend the church.
If everyone is called “Mr.” Mrs." Ms." “Miss,” etc, then it is unclear who is actually receiving a salary as a hired staff member, and who is a lay volunteer. That’s why you’ll hear the term “pastor” used. After all, pastor simply means “shepherd.” It doesn’t mean “Jesus, the Good Shepherd.” It just means “shepherd,” and that’s what these hired people are–shepherds who are in charge of leading the congregation in a specific area (e.g., youth, music, children, visitation, etc.)
In the churches where everyone is called “Brother” or “Sister,” you will sometimes find that they don’t recognize that anyone in the church has any more authority than anyone else. Someone is usually hired who has been through seminary and has credentials that allow them to marry and bury people. But that person is simply viewed as another “elder” in the church.
That’s another term that’s used in some denominations–“elder.” And sometimes you’ll hear “deacon.”
But these titles don’t matter, and they shouldn’t upset Catholics. Think of it this way: Different families have different “names” that they call their family members. E.g., in some families, it’s “Grandmother”, while in other families, it’s “Grandma”, or “Granny” or “Nana” or “MeMa,” or whatever. She’s still your beloved relative! The name isn’t an issue.