Fit combination locks on lorries bound for England

I AM struggling to understand how the doors of lorries can be opened at service stations in France.

Surely if used by hundreds of truckers there must be queues for the petrol pumps so wouldn’t other drivers see this happening and sound their horns?

But more importantly, why are the doors not securely locked?

If the traffickers have equipment to break the locks then wouldn’t it make sense for all vehicles to be fitted with combination locks that only the driver knows the numbers to? And if the doors are forced open then alarm bells would sound in the cab. Wendy Leftwich, Caldy, Merseyside