Maybe the keys were not securely locked up inside the dealership?
(And maybe workers’ account passwords were on post-it notes over their desks?)
They’re usually going to be in a key cabinet or safe like this: https://www.youtube.com/watch?v=JaEE991cr5s
But those things don’t all have adequate shielding, so you can use a signal booster to make off with a keyless car. The other option is that they simply broke into the key dispenser and took all of them; they’re often not that heavily armored, there are more heavily protected cheap ATMs.