Even before the bronze age, armies often used lightly armoured scouts who could move quickly and quietly.
I don't think the lightly armoured HMMWVs that were supplied were accidentally lacking armour, and that the soldiers were fixing a problem with them that the military should have noticed but didn't. I think it was an intentional choice to have a lightly armoured recon and transport vehicle and that the soldiers didn't agree with that choice and wanted a heavily armoured vehicle instead.
Sometimes soldiers know what they need better than the upper brass. On the other hand, sometimes the upper brass wants to save money. Sometimes they want a vehicle that's quick and hard to spot, rather than one that's really safe for its occupants.
It's probably a bad sign, especially in an all-volunteer military, when the soldiers refuse to accept the equipment they're given and insist on modifying it because they assume the brass are idiots and gave them something defective.