I will sing the wondrous story Acapella Church of Christ

This is the Westside Church of Christ singing Hymns of praise to Jesus Christ our savior. We are located at
1705 Starview Dr
Salem, VA 24153

Our website http://www.westsidecofc-salem.com/

Speaking to one another in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord (Ephesians 5:19).

Let the word of Christ dwell in you richly in all wisdom, teaching and admonishing one another in psalms and hymns and spiritual songs, singing with grace in your hearts to the Lord (Colossians 3:16).

Why do some churches teach that it is wrong to use musical instruments to accompany our singing during Christian worship assemblies when the above verses don't precisely forbid it?

I think most will agree that God has specifically instructed (even "commanded") Christians to sing as part of the worship that He expects (even "demands"). Since He has not commanded nor even suggested to us to play musical instruments in worship, we can be absolutely certain that if we don't use musical instruments, then He will be pleased with Christians singing if their worship comes from the heart.