The Jews did not use instruments in worship after the destruction of Solomon’s Temple. 
They consider the use of instruments in the synagogue to be wrong because they were specifically part of the temple worship. 

So for five hundred years before the beginning of the church, and for almost five hundred years afterward in the church, instruments other than the human voice were not used. 

If the apostles and the church of the first century did not use instruments in worship, then their controversial addition five hundred years later seems more and more like one of those additions made by men.

The Bible never requires instruments. Even if they were allowed in the temple worship, they were never required. I know of few people who would say that we can worship God by singing, but it must be accompanied by an instrument. Most would say it is acceptable to sing without them. If it is acceptable to sing without them, and possibly questionable to sing with them, then why not be safe and sing without them? 

If the Jews themselves would not sing to God with them, other than in the Temple, why should we?