Matthew quoted old testament often to prove Jesus fulfilled the prophesies.
John's entire ministry was to prepare people for Jesus' arrival.
John wasn't living a prosperous life. He was the exact opposite of a prosperity preacher.
His appearance may have scared some people. He wasn't the normal preacher.
True repentance requires you to own up to your sin. Not justify or excuse it. Jesus won't accept excuses or justification. Only us admitting our sin, humble ourselves and ask for forgiveness. Not what most are hearing from the pulpit today. Thankfully where I go to church he calls sin, sin.
In verse 7 those coming weren't coming in repentance. That is why he called them out. They were just following the crowd. Not repenting at all.