I think you're judging them with the benefit of hindsight as regards issues like providing some sort of pension or plot of land for legionaries after their retirement. Augustus was in a position to formalise this because he was, essentially, the greatest of the 'rule breakers', and ultimately was in a position to become the chief 'rule maker' (I'm using those terms simply on the grounds that it's 02:00 and I find them funny). To an aristocrat of say circa 100BC, a man who came from a coccooned, insulated, way of life, who had grown up in a world where legionaries could be counted on to serve the state whenever the state demanded it of them, and who were men of property and substance, who had a vested interest in Rome's wellbeing (that is, according to the dismissive views of a Roman aristo when it came to the proles [again, it's 02:05, sorry]) Marius' decision to allow the head count to enlist would have been tantamount to revolution. Therefore, to actively set them up for their old age, when all they'd done was provide a public service was out of the question. Similarly, later in the first century BC, they may have argued that 'bribing' Romans to remain loyal to the state was an anathema. Personally, I think they were shortsighted, but, I can understand their reasoning.