Iron Golems not spawning even when all conditions are met.

My friends and I have noticed that Iron Golems are not spawning properly. We built up a village with at least 20 beds, 10 villagers, meeting area, bells, 80 - 100% of villagers have jobs, traveled at least 80 blocks away, 50 blocks vertically, day and night cycle. But still no Iron Golem spawn.