We cannot speak for for all 'male pastors.' At our assembly, women minister in a variety of ways. Some speak in various venues, others serve behind the scenes, and some work mostly with children. A women's number one ministry is to her husband and children.
From a biblical perspective, all believers are called into ministry by the gospel. There is no such thing biblically as 'The Ministry,' a select group within a church who are set apart from the rest of the body. We are all one in Jesus Christ (Galatians 3:26-28). The gospel is certainly not a call to just sit on a pew; it is a call to serve the Lord. That is the heart of ministry. God calls both men and women to this.
The one difference between the work of men and women concerns pastoral oversight. This is to be done by men only (see our article called Why Women Cannot Serve in Oversight on Shelf 2 of the Apostolic Free Library). Some consider speaking from behind a pulpit to be equal to exercising pastoral authority. This is a Roman Catholic concept that continues to linger among some apostolics. This may explain your observation that some male pastors won't allow women to speak from the pulpit.