Trial spawners use snake case in their block entity tags, while mob spawners use pascal case.

Example: /give @s minecraft:trial_spawner[block_entity_data= {id: trial_spawner, spawn_data:{entity:

}}]

Versus: /give @s minecraft:spawner[minecraft:block_entity_data={id: mob_spawner, SpawnData:{entity:

}}]

Pascal case also applies for the other spawner tags, like RequiredPlayerRange, MaxNearbyEntities, etc.