This is an unfortunate translation in the King James and other Bible versions of the Greek phrase óchlou polloú. This combination can mean "much [or many] people," but it also has a variety of other English synonyms. Since the Bible elsewhere plainly tells us that the reward of the saved is this earth (see Matthew 5:5; Psalm 37:22; Romans 4:13; Revelation 5:10; etc.)—not heaven—it is evident that another rendering of this Greek phrase should have been chosen.
Many modern translations, for instance, the New King James, the New American Standard, English Standard, New International, and the Revised Standard versions render óchlou polloú as "great multitude." The Revised English Bible translates it as "vast throng," the Moffatt translation renders it as "great host," the Amplified New Testament uses "great crowd," and the J.B. Phillips version has it as "vast crowd."
These translations best convey the meaning of the original Greek. Thus, the "people" of Revelation 19:1 are not humans, as we normally construe the word to mean. John is actually describing the "host, crowd, throng, or multitude" of heaven. This verse is speaking thousands or tens of thousands of angels who sing praises to God before His throne in heaven (Revelation 5:11-12).