Revivals often relate to sociological phenomena. In the Old Testament we noted that many of the revivals had political oppression or similar sociological phenomena as preparation. Jerusalem had many people in its pilgrim throngs who longed for a Messiah to end the Roman oppression. Just because one can point to these phenomena does not mean that revival can be explained away. God prepares people for revival in many ways, not least of which is through various forms of oppression.
People join in revivals for a variety of reasons.
Some people join because their hearts are truly turning to God. Still others join because they want to be in on what is happening or simply to be close to the power of the leader. Involvement in revival phenomena doesn't reliably measure a person's true heart condition. Revivals may start suddenly or may develop gradually. Pentecost started with an explosive one-day conversion of 3,000 people.