The Chest and Hopper minecarts don't have a Lock data tag, like in their solid homologue.

(I'm opening the minecart in the 2nd screenshot without the redstone named "TestKey".)

Steps to Reproduce:

• Run the following commands:

/summon minecraft:chest_minecart ~ ~ ~ {Lock:"Test"}
/summon minecraft:hopper_minecart ~ ~ ~ {Lock:"Test"}

→ Notice how you are able to open both the hopper and chest minecart and that the "Lock" data tag doesn't exist for these entities.