I reckon saint Peter quoted Joel because the day of Pentecost was the fulfilment and that's why saint Peter said "For these aren’t drunken, as you suppose, seeing it is only the third hour of the day. But this is what has been spoken through the prophet Joel: ‘It will be in the last days, says God, that I will pour out my Spirit on all flesh. Your sons and your daughters will prophesy. Your young men will see visions. Your old men will dream dreams. Yes, and on my servants and on my handmaidens in those days, I will pour out my Spirit, and they will prophesy. I will show wonders in the sky above, and signs on the earth beneath; blood, and fire, and billows of smoke. The sun will be turned into darkness, and the moon into blood, before the great and glorious day of the Lord comes. It will be that whoever will call on the name of the Lord will be saved.’" (Acts 2:15-21 WEB) It's what happened when the Holy Spirit came upon the Church fifty days after the resurrection of our Lord, Jesus Christ.