1) Because it is not easy to talk to somebody you cannot see.
2) Because you do no know what to pray for. (Romans 8:26)
3) Because it is not easy to talk to somebody who does not say anything back.
4) Because you are spiritually discharged as you got about your daily life. (1 Corinthians 14:4)
5) Because otherwise most of your prayers will be directed by the flesh and by foolishness. (Acts 2:4)
6) Because without the anointing to pray, everything you say is listened to by the devil. (1 Corinthians 14:1)
7) Because you will know the mind of the Spirit. (1 Corinthians 14:13)
8) Because it is difficult to pray for a long time. (Mark 1:35)
9) Because your mind wanders when you pray. (1 Corinthians 14:28)
10) Because in the natural you may not have a grateful attitude. (1 Corinthians 14:17)