Why does only one person "teach" during a church meeting? Consider these scriptures:


  "And don’t get drunk with wine, which leads to reckless actions, but
  be filled by the Spirit: speaking to one another in psalms, hymns, and
  spiritual songs, singing and making music from your heart to the Lord,
  giving thanks always for everything to God the Father in the name of
  our Lord Jesus Christ, submitting to one another in the fear of
  Christ." Ephesians 5:18-21
  
  "Let the message about the Messiah dwell richly among you, teaching
  and admonishing one another in all wisdom, and singing psalms, hymns,
  and spiritual songs, with gratitude in your hearts to God." Colossians
  3:16
  
  "What then is the conclusion, brothers? Whenever you come together,
  each one has a psalm, a teaching, a revelation, another language, or
  an interpretation. All things must be done for edification." 1
  Corinthians 14:26
  
  "For you can all prophesy one by one, so that everyone may learn and
  everyone may be encouraged." 1 Corinthians 14:31


Why is it that only one person teaches during the meeting of the saints (the church meeting)? Isn't this contrary to what scripture is teaching? If it is not contrary to scripture, is there any evidence in the New Testament for having a "single teacher" in the church meeting? 

I can't seem to find any evidence for this church practice in Scripture, so I'm wondering if this is a church tradition that is perhaps against the teachings of Scripture.

What I understand from the above passages (even read in context), is that everyone in the church has a responsibility to exercise the gifts that have been imparted to them by the Holy Spirit. If we are not participating in the active leadership of this meeting (by teaching, prophesying, and singing, for example), then we aren't we being passive and not fulfilling the call of the church?
I attended meetings of the Vineyard for a period of a year and the members there exercised the gifts of the Spirit, with multiple people, one at a time, giving revelation and prophesying, tongues and interpretations. Then they bunched together and prayed for healings for the afflicted.

I attended a Brethren-inspired gathering for about 8 years. There, they encouraged multiple brothers to get up and speak on the same Sunday morning. The one with little experience spoke for 10 minutes; those with more ability, 15-20 minutes; those with gift, 30 minutes. (So when I say that I have preached for 8 years, people think I'm a pastor!) In this same church, the singing was not led by a choir or worship leader, but members of the body spoke out a hymn number between individual bouts of verbal worship, and we sang that. 

Because these settings are outside of any traditional settings I've witnessed in mainline denominations, I can only conclude that historical tradition has dictated the idea of a single speaker. Also, it makes sense for the pastor to do all the speaking because he is paid to do so and (generally) has the ability to communicate the things of God well. In a regular church service where many are present, it certainly makes for a more controlled environment when the message isn't interrupted with questions or comments (I've attended one of those, too!)