Villagers spawned on world generation have a lower followrange(16) than villagers spawned by any other means(48), villagers with a lower follow range will often fail to find a bed or workstation and keep standing still during nighttime, often resulting to their death by mobs.

You can see the NBT for yourself by using F3 + I on a villager.

Villager which has spawned on world generation:

/summon minecraft:villager -407.42 62.94 -286.22 {Brain: {memories: {"minecraft:meeting_point":

{pos: [I; -410, 64, -283], dimension: "minecraft:overworld"}

}}, HurtByTimestamp: 0, Attributes: [{Base: 20.0d, Name: "generic.maxHealth"}, {Base: 0.0d, Name: "generic.knockbackResistance"}, {Base: 0.5d, Name: "generic.movementSpeed"}, {Base: 0.0d, Name: "generic.armor"}, {Base: 0.0d, Name: "generic.armorToughness"}, {Base: 16.0d, Modifiers: [

{UUIDMost: 4630429775339866964L, UUIDLeast: -9196332054275879034L, Amount: -0.12084116038811184d, Operation: 1, Name: "Random spawn bonus"}

], Name: "generic.followRange"}, {Base: 0.0d, Name: "generic.attackKnockback"}], FoodLevel: 0b, Invulnerable: 0b, FallFlying: 0b, ForcedAge: 0, Gossips: [], PortalCooldown: 0, AbsorptionAmount: 0.0f, LastRestock: 0L, FallDistance: 0.0f, DeathTime: 0s, Xp: 0, LastGossipDecay: 287L, HandDropChances: [0.085f, 0.085f], PersistenceRequired: 0b, Age: 0, Motion: [-0.006275382081949357d, -0.0784000015258789d, -0.004560577165710219d], Health: 20.0f, LeftHanded: 0b, Air: 300s, OnGround: 1b, Rotation: [316.85596f, 0.0f], HandItems: [{}, {}], RestocksToday: 0, ArmorDropChances: [0.085f, 0.085f, 0.085f, 0.085f], Fire: -1s, ArmorItems: [{}, {}, {}, {}], CanPickUpLoot: 1b, VillagerData: {profession: "minecraft:none", level: 1, type: "minecraft:plains"}, HurtTime: 0s, Inventory: []}

 

Villager which has spawned by a spawn egg:

/summon minecraft:villager -400.50 63.00 -312.50 {Brain: {memories: {}}, HurtByTimestamp: 0, Attributes: [{Base: 20.0d, Name: "generic.maxHealth"}, {Base: 0.0d, Name: "generic.knockbackResistance"}, {Base: 0.5d, Name: "generic.movementSpeed"}, {Base: 0.0d, Name: "generic.armor"}, {Base: 0.0d, Name: "generic.armorToughness"}, {Base: 48.0d, Modifiers: [\{UUIDMost: -1989428605440998311L, UUIDLeast: -8887357040257394265L, Amount: -0.08023876591329335d, Operation: 1, Name: "Random spawn bonus"}], Name: "generic.followRange"}, {Base: 0.0d, Name: "generic.attackKnockback"}], FoodLevel: 0b, Invulnerable: 0b, FallFlying: 0b, ForcedAge: 0, Gossips: [], PortalCooldown: 0, AbsorptionAmount: 0.0f, LastRestock: 0L, FallDistance: 0.0f, DeathTime: 0s, Xp: 0, LastGossipDecay: 532L, HandDropChances: [0.085f, 0.085f], PersistenceRequired: 0b, Age: 0, Motion: [0.0d, -0.0784000015258789d, 0.0d], Health: 20.0f, LeftHanded: 0b, Air: 300s, OnGround: 1b, Rotation: [62.95449f, -23.903345f], HandItems: [{}, {}], RestocksToday: 0, ArmorDropChances: [0.085f, 0.085f, 0.085f, 0.085f], Fire: -1s, ArmorItems: [{}, {}, {}, {}], CanPickUpLoot: 1b, VillagerData: {profession: "minecraft:none", level: 1, type: "minecraft:plains"}, HurtTime: 0s, Inventory: []}