There are many religions because God is not presently trying to teach the world the truth. Jesus said He was not sent to convert the world. "That seeing they may see, and not perceive; and hearing they may hear, and not understand; lest at any time they should be converted, and their sins should be forgiven them," Mark 4:12.
When Christ establishes His earthly kingdom, then God will teach everybody the one, true religion. Isaiah 11:9, "the earth shall be full of the knowledge of the LORD, as the waters cover the sea." Jeremiah 31:34 (CSB), "No longer will one teach his neighbor or his brother, saying, ‘Know the LORD,’ for they will all know me, from the least to the greatest of them” — this is the LORD’s declaration. “For I will forgive their iniquity and never again remember their sin."
Any religion which is not based on the Bible is false. Satan, the father of lies, presents lies as truth. He doesn't want men to know the wise, just, powerful, and loving God of the universe. 2 Corinthians 4:4, "whose minds the god (Satan) of this age has blinded, who do not believe, lest the light of the gospel of the glory of Christ, who is the image of God, should shine on them."
Thankfully, all these lies will end when the kingdom is turned over to the Father and Satan is finally destroyed. 1 Corinthians 15:24 (ESV), "Then comes the end, when he delivers the kingdom to God the Father after destroying every rule and every authority and power."