Why were the Triarii differently equipped?

[Corvus]

Maybe the reason for the different armor, is not only the wealth, but also like mentioned here their function to hold the line.
I can imagine that their armor was heavier, and offered more protection.
If I would be a hastati or principes, I would try to use more lighter armor, to be more fast and have more movement

I also think that at some point in roman history, the legionaries got supplied by the state with armor and it was not according to wealth, but to experience and years of service in what of the 3 classes a citizen served