As far as the linothorax, they decay over time. It's a relatively easy form of armor to fabricate, and provides a good deal of protection. We find many, many waistbands from such suits of armor, because they're made out of scales (generally, at least the more expensive ones probably have this feature), but no full suits. Must we find a full suit of linen armor for you to believe they were there?

Now, a soldier with an (expensive) metal helmet, an (expensive) sword, javelins, a large spear, greaves (expensive), good boots, and all that other stuff, is going to, what, not have enough drachmae left over for some inexpensive but effective body armor?