You seen how many fail? They were good when they left the factory. I've watch techs who have no clue about ESD, again and again. Ineptness is not a desirable skill set.
See how small that card is? If it has any onboard protection it is very limited because of this and they're a dime a dozen.
ESD event damage is cumulative and after one ESD or more event(s) failures can be instant or caused over time by the normal device voltages ie unpredictable failures. Once the electrons punch through the damaged micron thin insulator, it becomes a conductor.
So just because it's working after being carelessly handle doesn't mean it hasn't been damaged. If it fails ESD damage during installation is the most probable cause as it's fairly well protected once in circuit. Even so I handle mobos with a wrist strap and a grounded ESD mat.
They worry about protecting the SIM controller.
Why? Because of user caused ESD events inserting SIM cards.
Devices have some level protection:
https://m.littelfuse.com/technical-resources_old/application-designs/circuits/sim.aspx
https://www.semtech.com/products/circuit-protection/esd-emi-filter-devices/eclamp2485t