Why were the Triarii differently equipped?

[JaM]

i think that depends on society from which you take that average men. Imagine today, only citizens who's wealth is above certain level would be accredited to enter army. it would depend on that wealth level, how well equipped that army would be (assuming they would need to buy own equipment as Romans had to) Well suited families (especially those with wealth over 10.000 drachmae) would be capable providing high quality equipment to all its members, as their survival would be the most important thing - another example (not sure if I already mentioned here) - during current crisis in Ukraine, government doesn't have enough of money to buy ballistic vests to all soldiers. Instead, they buy their own. Normal vest costs around 1500euros, while average monthly pay at Ukraine is around 300 euros, which mean majority of people cannot buy it on their own, so they go and sell their cars, flats or any possible wealth, just to buy a ballistic vest for their son, to give him a chance to survive in war.. ultimately, his life is more precious to them than money..(btw, those who cannot buy it, are using any other form of protection, they for example are buying hardened steel plates cut off from military vehicles and use them as addon armor..) I think same behavior would apply in ancient times as well. If your family has money, they would buy appropriate protection to all its members going into war, just because you are youngest, it doesn't mean they would give you worse armor, some would do the exactly the opposite, and father would give his armor to his youngest, who would be serving in first line.. (as a father, you really want to protect your kids..)

All this social background needs to be taken into consideration...