You ask why? How about deal with all the scriptures I gave proving why not?
Speaking in tongues was a gift given, a sign, given (Isaiah 28:11) during the laying of the foundation of the Church (Hebrews 2:4). It was a sign to the Jews (Acts 2:6). Speaking in tongues has served God's purpose, God has given the sign (1Cor 14:21), and God has laid the foundation (Eph 2:20). Speaking in tongues by the Gentiles showed the Jews that God granted even the Gentiles repentance unto life (Acts 11:18). Tongue speakers spoke mysteries (1 Cor 14:2); consequently, the mystery of the gospel has been given (Eph 6:19). Speaking in tongues is the language of angels (1 Cor 13:1), angels minister to humans (Hebrews 1:14). Humans are to understand speaking in tongues in earthly languages (Acts 2:6, 11). Speaking in tongues would be “stilled” (1 Cor 13:8).
The believers in the Bible times who spoke in tongues, they spoke in tongues supernaturally. The believers who supposedly speak in tongues nowadays, they speak gibberish and believe God turns their gibberish into supernatural language, and that is a false doctrine.