why did Paul address speaking in tongues as a problem in 1 Corinthians?
Paul addressed tongues because the Corinthian church remained carnal and spiritually immature, and the practice had become a disruptive problem rather than evidence of spirituality. It upset the local church's function and caused disorder, so he had to correct it.
Les explains that in 1 Corinthians Paul was dealing with a church that was still carnal and had not grown spiritually. From chapter 1 onward, Paul addressed divisions over following Peter, Apollos, or Christ, lawsuits among believers in pagan courts, and gross immorality. The tongues phenomena likewise had become a problem: it upset the function of the local church and caused disorder, so Paul had to address it, not as an aspect of their spirituality.